In the large bowl of a stand mixer fitted with the paddle attachment, or in a large bowl with a hand mixer, beat together the butter, sugar, vanilla extract, mint extract, salt, and green food coloring on medium speed. Beat until smooth and well blended.: Expect a soft, pale mixture that smells richly of butter with an immediate lifted hint of vanilla and mint. The texture should be light, not greasy, as the sugar incorporates air and the butter takes on a slightly whipped look. This aeration is why I use medium speed, it helps build body without overheating the butter. If you see streaks of unmixed butter or lumps of sugar, scrape the bowl and continue beating until the mixture looks homogeneous, smooth and glossy. A common mistake here is working with too warm butter, which makes the mixture oily; if that happens, chill the bowl briefly then resume. The color will begin to show from the green food coloring but should still be soft and pastel at this stage.
Turn the power to low and mix in the flour just until the dough comes together.: You will feel the dough change from loose to slightly shaggy, and the sound of the mixer will quiet a bit as the all purpose flour absorbs the butter. The goal is to avoid over mixing so gluten does not develop and make the cookies tough. Stop as soon as the dough forms large clumps and pulls away from the bowl sides. If the dough looks overly dry, a teaspoon of cream or two can be added briefly, but usually the balance is correct. Avoid the impulse to mix on high, which will make the dough dense and ruin the tender shortbread texture.
Lay out a 24" long or so piece of wax paper or parchment paper and sprinkle lightly with flour.: The sensory cue here is a faint dusty feel to the paper that will prevent sticking. The lightly floured surface gives the dough a nonstick bed for rolling. If you skip this step the dough can adhere to the paper and tear when you try to roll it, creating uneven logs and frustrating slicing later. Use just a dusting of flour to keep the exterior from getting cakey.
Carefully turn the dough onto the paper, then, with floured hands, roll the dough into a log about 2 1/2 inches in diameter.: As you roll, notice the dough warming slightly from your hands, becoming smoother. Aim for a consistent diameter so slices bake evenly. If the dough becomes too soft or sticky, pause and chill briefly so it firms up again. Uneven logs lead to cookies that bake differently, so take a moment to smooth and compress as you roll to create a taut, even surface.
Roll the dough into the wax or parchment paper, then twist the ends of the paper tightly so the dough forms a round, taut log.: You should feel a gentle tension as you twist, similar to wrapping a candy. This helps the log keep its shape in the chill, preventing flat spots. The wrapped log also protects the dough from drying out in the fridge. A mistake is to wrap too loosely, which can let edges sag and cause uneven slices; twist snugly but not so tight that it deforms the log.
Refrigerate for 1 to 1 1/2 hours, until firm.: The dough should feel solid to the touch and cool through to the center. Chilling allows the butter to re firm, which controls spread and preserves the shortbread texture. When you press the log it should give slightly but not indent deeply. If you rush this step the cookies will spread thin and lose their tender, crumbly interior, so be patient and trust the hour to firm things up.
Preheat oven to 325 degrees Fahrenheit.: Heat until the oven maintains temperature, which ensures even browning. You will notice a warm, dry air when you open the oven; that steady environment is what helps shortbread develop a delicate edge without burning. The moderate temperature favors slow coloring for a golden edge while keeping the centers pale and tender, which is the hallmark of proper shortbread.
Remove dough from the refrigerator and cut into approximately 18 slices about 3/8" thick. If the dough gets crumbly, let it sit at room temperature for a couple of minutes then try again.: The slices should hold their shape when cut and have clean edges. If they crumble, they are too cold or brittle, so a brief rest softens them just enough to slice cleanly. Pay attention to thickness so all cookies bake uniformly; uneven thickness leads to some cookies being done before others. Use a sharp knife and a gentle sawing motion to prevent smashing.
Lay about one inch apart on an ungreased cookie sheet.: You should hear a very faint clink as the cookies touch the metal briefly while you place them, and they should sit with space to allow minimal spreading. The one inch spacing is intentional to keep them nearly touching when finished, which preserves edges. Avoid overcrowding the sheet, which creates uneven heat and can produce cookies that bake inconsistently.
Bake for 15 - 20 minutes, until the edges begin to turn brown.: Use visual cues rather than strict timing, because ovens vary. The aroma will shift from buttery to slightly toasted, and the edges will ginger to a pale golden brown while the centers remain light. Remove closer to 15 minutes for more tender centers, or up to 20 for crisper cookies. A common error is leaving them until the centers darken, which indicates overbake; aim for gentle edge coloring.
Remove from oven and let sit for a couple of minutes, then transfer to a wire rack to let cool completely.: Letting them rest on the sheet helps them set slightly so they do not fall apart when moved. Then transfer to a wire rack where air circulates, preventing sogginess and ensuring even cooling. You will notice the scent intensify as they cool, and the texture firms to that signature shortbread snap.
In the bowl of a stand mixer fitted with the whisk attachment, or in a large bowl with a hand mixer, beat the butter on medium speed until creamy, about 30 seconds.: The butter will go from dense to pale and smooth, and a light, airy presence will form. This initial cream creates the base structure for the frosting. If the butter stays lumpy, it may be too cold and will not incorporate the powdered sugar well; let it warm slightly and try again to avoid a gritty frosting.
Turn the mixer speed to low and slowly pour in the powdered sugar. Once the powdered sugar is incorporated, mix on medium for about 30 seconds.: Slowly adding powdered sugar prevents a cloud of dust and allows it to blend into a stable, silky body. Once combined, the mixture should be smooth and no longer grainy. If it looks dry, a small splash of heavy whipping cream can help, but add sparingly to maintain piping structure.
Add the vanilla extract, peppermint extract and pinch of salt. Mix for another 30 seconds.: The aroma shifts here as the mint becomes noticeable against the sweet frosting. The pinch of salt sharpens the sweetness and brings clarity. Taste cautiously because extracts can be potent; overdoing the mint can overshadow the shortbread's buttery essence.
Add the heavy whipping cream and beat on medium until light and white, about three minutes.: As you beat, the frosting will lighten and become nearly fluffy, with a texture perfect for piping. The heavy whipping cream also makes the frosting silky and less dense, which balances the cookie. If the frosting seems too loose, beat a bit longer or add a touch more powdered sugar; if too stiff, a teaspoon of cream loosens it without making it sloppy.
Place the frosting in a pastry bag (or Ziploc bag - it works) fitted with a star icing tip.: You should feel the frosting glide into the bag and hold its shape, not drip. The star tip creates pretty ridges and helps the frosting mimic the look of a thick shake swirl. Avoid overfilling the bag which makes it hard to control; half full gives the best control and appearance.
Squeeze the icing onto the cooled shortbread. I start with the outer circle and end at the top.: The frosting should hold a defined shape and look glossy. Start on the outside so you build a neat edge, then work inward in a spiral to create a pleasing mound. A common oversight is piping onto warm cookies, which melts the frosting; always ensure cookies are thoroughly cool to preserve the decorative swirl.
Top each cookie with a half drained maraschino cherry.: The cherry adds a sweet, slightly tangy contrast and a visual pop of color. Press gently so it nestles into the frosting without sinking. Use the drained halves to avoid excess syrup that can make the frosting run. Placing the cherry while the frosting is still slightly tacky helps it adhere.
Cookies keep in an airtight container at room temperature for three or four days.: Stored properly, they maintain texture and flavor. You will notice the frosting soften slightly over time but the shortbread should remain tender. If storing longer, refrigerate and let come to room temperature before serving for best texture. A common mistake is stacking without parchment between layers, which causes frosting to stick and mar the decoration.