To make the cookies: To the bowl of a stand-up mixer, add the butter, granulated sugar, powdered sugar and salt. Beat until light and fluffy, about 3 minutes. Add the egg, egg yolk, vanilla paste or extract and beat once more until combined. In two batches, add the flour, being sure each addition is combined before adding the next one. Divide the dough in half, transfer it to two sheets of plastic wrap (it’ll be quite soft!), shape into a disc and transfer to the fridge. Allow to chill for about 1 hour.: The bowl fills with the sweet, buttery scent as you cream the butter and sugars together, a light hum from the mixer as air collapses into a fluffy pale mass, which signals proper aeration. The texture should be visibly lighter and slightly voluminous, a few minutes of beating usually does this. When you fold in the egg , egg yolk , and vanilla , a richer aroma develops and the batter becomes silkier, indicating cohesion. Adding the all purpose flour in two batches prevents overworking the dough, which would toughen the cookie; you want just enough mixing for a uniform dough. A common mistake is adding all the flour at once and continuing to mix aggressively, which creates a dense texture. If the dough feels too soft to handle, chilling will firm it up and make rolling simpler.
Turn the oven up to 375 degrees F. Line two baking sheets with parchment paper and set aside.: A cool, slightly firmer dough is easier to shape, so divide and wrap each portion in plastic wrap, smoothing into discs so they chill evenly. The refrigerated dough firms and holds moisture, which minimizes spreading during baking, and it gives the butter time to solidify so the cookies bake with a tender interior and defined edges. One hour chilling is usually perfect; shorter chilling can leave the dough too soft, and much longer chilling can make rolling more work. Avoid cutting corners here, because skipping the chill often produces flat, misshapen cookies.
Remove the first disc of dough from the fridge. Allow to come to room temperature for about 5 to 10 minutes. Liberally flour a rolling pin and work surface. Roll out the cookie dough to a 1/8-inch thickness. Stamp out the cookies using a 3-inch circular cookie cutter and cut out holes in the center using a 1/2-inch cutter (I found a piping tip to be the best for this). Transfer the cookies to the baking sheet, spacing them about 1-inch apart (these spread slightly). Re-roll the scraps to get a few more cookies, if you like. Repeat with the second disc of dough.: Preheating to the correct temperature ensures the cookies set quickly at the edges and maintain a slightly soft center. You will notice the oven door closing on a steady heat that helps the cookies color evenly. Using parchment on the sheets prevents sticking and promotes even browning on the bottom. A mistake to watch for is placing cold baking sheets in the oven with cookie dough on them, which can alter bake time; allow sheets to come to oven temperature if you preheat with them inside.
Bake the cookies, one baking sheet at a time, for about 8 to 10 minutes, until lightly golden brown around the edges. Cool on the baking sheet before transferring to a cooling rack. Repeat with the remaining cookies.: Allowing it to rest for about 5 to 10 minutes softens it just enough to roll without tearing, giving a cool, slightly pliable feel under your palms. Generously flouring the work surface and rolling pin prevents sticking while rolling the dough to a 1/8 inch thickness, which yields a delicate, even bake where the center remains tender and the edges gain a light crisp. Cutting with a 3 inch cutter and using a 1/2 inch cutter for the center creates the classic shape, and transferring the rounds to the sheet should be done with a thin spatula to avoid distortion. A common problem is rolling too thin or too thick; inconsistent thickness leads to uneven baking, so check visually for uniformity across the sheet.
For the record, my favorite way to melt chocolate is to put it in a glass bowl and microwave it for a minute and stir until smooth. You can also nestle a glass bowl atop a saucepan that’s filled with a few inches of simmering water. Add the chocolate to the bowl and allow to melt. Stir until smooth.: As the cookies bake, the kitchen fills with a warm, toasty butter aroma and the edges begin to take a light golden tone, the main visual cue they are ready. They typically need about 8 to 10 minutes; you will see a slight color at the edges while the centers remain pale. Cooling briefly on the baking sheet lets them set without being fragile, then moving to a cooling rack finishes the process and prevents condensation on the bottoms. A common misstep is overbaking to achieve color; that kills the tender center, so remove them when edges are lightly golden and centers still look slightly soft.
When the cookies are cool, drop the bottom side into the chocolate, allowing any excess to run off (I found a bench scraper to help in getting the excess off). Transfer to a baking sheet with parchment. Repeat with the remaining cookies.: The chocolate takes on a glossy sheen as it loosens into a smooth pool, whether you microwave in short bursts or use a double boiler method where steam warmth gradually softens the chips. A wooden spoon or spatula should glide through the melted milk chocolate chips with a satin feel, and a breath of chocolate aroma will fill the air. If the chocolate seizes or becomes grainy, it usually means it overheated; add a tiny splash of neutral oil or warm cream and stir gently to restore gloss. Melting too quickly is the typical error, so patience here pays off for silky dipping and piping.
Pour the remaining chocolate into a piping bag. Snip off the tip and create chocolate stripes. Do the best you can—mine weren’t perfect! Transfer to the fridge to set for 10 minutes. Serve with milk.: When the cookies are cool, dipping the bottom side into the warm milk chocolate chips delivers a satisfying click and swirl as excess chocolate runs off back into the bowl. Using a bench scraper to tap off extra keeps the bottoms tidy and evenly coated. Transfer the dipped cookies onto parchment to set, and the contrast between the matte cookie and glossy chocolate is obvious and pleasing. A common mistake is dipping while the chocolate is too cool and thick, which yields clumpy coverage, so keep the chocolate fluid but not scorching hot.
Pour the remaining chocolate into a piping bag: The remaining milk chocolate chips should flow smoothly through a small snip in the bag, creating thin stripes across the cookies. The tactile rhythm of moving from cookie to cookie, applying steady pressure, results in even lines that harden with a snap in the fridge. Even if the stripes are imperfect, they add a handmade charm. Avoid overfilling the bag which can cause uncontrollable splats, and chill the cookies for about 10 minutes to set the design.
Transfer to the fridge to set for 10 minutes: The coolness firms the chocolate quickly, giving you a neat finish and a crisp snap when bitten. It also helps the stripes keep their shape during storage or transport. Leaving them at room temperature too long before serving can soften the chocolate and reduce visual appeal, so a short chill is both practical and aesthetic.
Serve with milk: Pairing the cookies with a cold glass of milk enhances the balance between sweet and buttery textures, and the milk acts as a palate cleanser between bites. The contrast of creamy milk and dense cookie is timeless, and I often notice guests deliberately dunking for that nostalgic feel. A mistake is offering warm drinks that can soften the chocolate prematurely, so I stick with cool or room temperature beverages.