Cookies

• Using an electric mixer, beat butter, sugar and salt in a large bowl, scraping down sides and bottom of bowl as needed, until light and creamy, about 3 minutes.
• Add egg yolks and vanilla and beat until incorporated, about 1 minute.
• Reduce speed to low, add 2 cups flour, and mix until incorporated. Dough will be semifirm but can be rolled out without chilling. If your kitchen is very warm and/or dough is sticky, pat it into a 1″-thick disk, wrap in plastic, and chill 15 minutes to let firm up before rolling out.
• Preheat oven to 350°.
• Roll out dough on a lightly floured sheet of parchment paper, dusting with more flour as needed to keep dough from sticking, to about ¼” thick.
• Punch out shapes as desired with lightly floured cookie cutters and transfer to 2 parchment-lined baking sheets, spacing 1½” apart.
• Pat scraps into a 1″-thick disk, wrap with plastic, and chill 10 minutes if soft. Repeat process.
• Bake cookies 10-15 minutes, rotating halfway through, until edges are golden brown.
• Let cookies cool 10 minutes on baking sheet, then transfer to a wire rack and let cool completely. 

Glaze

• Whisk 1 cup powdered sugar, 3 Tbsp. milk, food coloring (start off with just a few drops and add more as needed), and half of salt in a small bowl until no lumps remain. Glaze should be the consistency of heavy cream; add more milk if needed.
• For a deeper color, whisk in more food coloring 1 drop at a time until desired color is achieved; adjust with milk if needed. Repeat with second food-coloring, remaining salt, remaining 1 cup powdered sugar, and remaining 3 Tbsp. milk, adjusting intensity of color as desired.
• Spoon 1 tsp. first glaze in the center of a small plate. Drizzle 1 tsp. second glaze over the first and use a toothpick to slightly swirl colors together; don’t go overboard. (If you want to decorate larger cookies, add 1 tsp. glaze to plate for each additional inch.)
• Gently press the top of a cookie into glaze, then lift up and allow excess glaze to drip back onto the plate.
• Using a toothpick, pop any air bubbles and swirl colors more if desired.
• Transfer to a wire rack set inside a rimmed baking sheet.
• Repeat with 2 more cookies, adding ½ tsp. of each color of glaze to plate before each cookie is dipped.
• The glaze will lose its swirly effect at this point. Clean plate and repeat process, decorating cookies in batches of 3 until all cookies have been glazed.
• Let sit until glaze is set, at least 2 hours.