In the bowl of a stand mixer, cream together pudding, butter, and granulated sugar until fluffy.: The bowl will smell sweet and nutty as the pudding mix and butter emulsify with the granulated sugar , and you will notice the texture shift from gritty to a smooth, satiny cream. This aeration traps tiny air bubbles that lighten the dough and help the cookies feel tender, so take time to reach a consistently fluffy texture. A common mistake is rushing this step, which results in dense cookies, so stop creaming only when the mixture lifts and holds a light sheen.
Scrape down sides and beat in egg. Turn the speed down to low and slowly mix in flour and salt until well-combined.: After scraping the bowl, the mixture will look more uniform, and when you add the egg , the batter will momentarily look glossy and more cohesive. The egg provides structure and moisture, and as it incorporates, the mixture should smooth out without streaks. If you skip scraping, pockets of unmixed pudding or butter will remain, causing uneven flavor and texture, so be thorough but gentle to avoid overbeating.
Spread dough onto a sheet of parchment paper. Cover with another sheet of parchment, and roll dough to approximately 1/8-inch thick. Transfer dough (on the parchment) to a cookie sheet and freeze for 20 minutes.: You will see the dough come together and lose some of its gloss as the flour absorbs moisture. Mixing on low prevents gluten from developing too much, which keeps the cookies tender rather than chewy. Stop as soon as there are no dry streaks, because overmixing creates tough cookies; the dough should feel slightly tacky but manageable.
Once dough has chilled, remove from the freezer and place parchment on counter. Remove the top parchment, flip it over, place it on the dough again, and flip the entire thing over. Remove the parchment that is now on top. (This step will help keep your cookies from sticking to the parchment after cutting.) Cut out rounds using a 3-inch round cutter. For half the cookies, cut out the center shape with a 1.5-inch clover cutter. Place cookies back on baking sheet and put in the freezer.: When the dough is spread on parchment, it will feel cool and pliable under the rolling pin. Press it into an even layer so it chills uniformly, which makes cutting cleaner later. If you spread it unevenly, you will have cookies that bake at different rates, so aim for a consistent thickness across the sheet.
Preheat oven to 350°F. Once the oven has preheated, remove cookies from the freezer, transfer to a clean parchment-lined baking sheet, and bake cookies for 6-8 minutes.: Rolling through the top parchment creates a smooth surface and prevents sticking, and you should see an even pale green sheet emerging. Thin edges will bake faster and can brown quickly, so check edges frequently. A common error is rolling too thin, leading to fragile cookies that tear when cut, so maintain the approximate thickness.
Let cookies cool on baking sheet for 2 minutes before removing to a wire rack.: The dough will firm up and the surface becomes cool and slightly stiff, which helps maintain crisp cut edges when stamping shapes. This chilling is crucial for clean windows and neat shapes. If you skip freezing, the dough can spread in the oven and lose its crisp outlines, so allow the full chill time for best results.
Once cookies are completely cooled, make the frosting. In the bowl of a stand mixer, beat together softened butter and powdered sugar. Add the vanilla paste and milk and beat until frosting is fluffy.: The chilled dough should feel solid but pliable. When you remove the top parchment and flip as instructed, the goal is to ensure the dough does not stick after cutting, producing clean releases. If the dough warms too quickly while you work, pop it back in the freezer briefly to keep shapes neat.
To fill the cookies, fit a pastry bag with an M 2 tip and fill bag with frosting. Flip over full cookie round and pipe frosting onto bottom, starting from the outside and working your way in, in a circular motion. Top frosted cookie with clover-hole cookie.: The clean clack of the cutter signals a crisp edge, and you will see tidy rounds lifting from the parchment. For half the cookies, use a 1.5-inch clover cutter to make the center window; the clover creates a charming peek at the filling. Press straight down and wiggle as little as possible to avoid distorting the shape; otherwise, the window may close up during baking.
To add sprinkles, fill clover hole completely with sprinkles. Gently press on sprinkles so they adhere evenly, then tip cookie onto a rimmed plate to remove excess sprinkles.: Returning the cut cookies to the freezer firms the edges again, ensuring they keep their shape when transferred to the oven. You will notice the dough goes from tacky to firm under your fingertips. If you skip this step, delicate shapes can slump and lose definition when baked.
Preheat oven to 350°F: The oven should reach a stable temperature so the cookies bake evenly and the bottoms set properly. A consistent 350°F produces a light, pale cookie with slightly bronzed edges, which is the visual cue to aim for. If your oven runs hot, check with an oven thermometer to avoid overbrowning.
Once the oven has preheated, remove cookies from the freezer, transfer to a clean parchment-lined baking sheet, and bake cookies for 6 to 8 minutes: During baking you will see the cookies puff slightly and the edges set, while the centers remain pale; that is your cue to remove them. The aroma of butter will fill the kitchen and the pistachio note will be subtle in the oven steam. Overbaking even by a minute can turn them dry, so watch closely in the final minutes.
Let cookies cool on baking sheet for 2 minutes before removing to a wire rack: Resting briefly lets the cookies finish setting so they do not break when moved. The bottoms will still be slightly soft but will firm quickly on the rack. If you try to move them too soon, they can bend or crack, so use a thin spatula and be patient for those two minutes.
Once cookies are completely cooled, make the frosting: As you beat softened butter and powdered sugar , the bowl will look snowy and the mixture will lighten in color. Adding the vanilla and milk yields a glossy, smooth frosting that smells sweet and aromatic. If the frosting is grainy, you may have added the powdered sugar too quickly, so beat until smooth and adjust milk in tiny amounts.
In the bowl of a stand mixer, beat together softened butter and powdered sugar: The texture will go from fatty to whipped as air is incorporated, and the sound of the mixer will change from a heavy grind to a lighter hum. This step sets the stage for a fluffy filling that pipes neatly into the clover windows. If your mixer splatters, reduce speed and scrape the bowl to keep the texture even.
Add the vanilla paste and milk and beat until frosting is fluffy: The vanilla deepens flavor while the milk softens consistency so it is spreadable and pipeable. The frosting should hold soft peaks and look silky. If it becomes too loose, add a touch more powdered sugar; if it is too stiff, a few drops of milk will rescue it.
To fill the cookies, fit a pastry bag with an M 2 tip and fill bag with frosting: Filling a bag gives you control and a clean presentation; the tip size helps the frosting nestle into the cavity without overflowing. You will feel the gentle resistance as you pipe, and the frosting should mound slightly. If the bag is overfilled it can be hard to control pressure, so refill in smaller batches for steadier piping.
Flip over full cookie round and pipe frosting onto bottom, starting from the outside and working your way in, in a circular motion: The circular piping creates a cushion that supports the top cookie and prevents spilling. You will see concentric rings of frosting building up, and the texture should be airy and stable. Piping too sparsely can lead to a flat sandwich, while overfilling causes frosting to squish out when you top with the window cookie.
Top frosted cookie with clover-hole cookie: Gently press the top cookie down until the frosting slightly peeks through the window, creating an inviting view. The sandwich should feel cohesive without forcing frosting out the sides. Pressing too hard flattens the filling and can squeeze out sprinkles if you plan to use them, so aim for gentle contact only.
To add sprinkles, fill clover hole completely with sprinkles: Pressing sprinkles in ensures they adhere to the frosting and form an even visual field in the window. Use a light tap to remove excess sprinkles and a rimmed plate to catch fall off. Overpacking sprinkles can make the top heavy and cause them to fall out easily, so aim for a neat, even layer.
Gently press on sprinkles so they adhere evenly, then tip cookie onto a rimmed plate to remove excess sprinkles: The final step polishes the appearance and reduces mess. A soft press ensures sprinkles nestle into the frosting and stay put during serving. If you skip removing excess sprinkles, the presentation looks messy and you will lose vibrant color when plating.