Servings: Makes 18 cookies
- 3 cups all-purpose flour
- 1/2 tsp. baking soda
- 1/2 tsp. baking powder
- 1/2 tsp. salt
- 1 3/4 sticks butter
- 1 1/4 cups sugar
- 2 large eggs
- 1 large egg yolk
- 3/4 cup buttermilk
- 1 Tbsp. pure vanilla extract
- 1 Tbps. freshly grated lemon zest
- 4 cups confectioners' sugar
- 1/4 cup milk
- 3 Tbsp. heavy cream
- 2 tsp. pure vanilla extract
- Red no-taste gel food coloring
To make cookies: Preheat oven to 350°. Sift flour, baking soda, baking powder, and salt into a large bowl.
In the bowl of an electric mixer fitted with a paddle attachment, cream butter and sugar until fluffy (about 2 minutes). Scrape down the bowl and add eggs and egg yolk one at a time, beating briefly after each addition. Scrape down the bowl again, and turn mixer to low. Add the flour mixture in 3 parts, alternating with the buttermilk in 2 parts. Scrape down the bowl; add vanilla and lemon zest, and mix on low speed for a few more seconds.
Using an ice cream scoop (about 1/4 cup), drop dough onto parchment-lined baking sheets spaced about 3 inches apart (6 cookies per sheet).
Bake for 17 minutes, rotating sheets between oven racks halfway through, until edges are golden brown and tops spring back when gently touched. Remove from oven and let sit for 5 minutes, then remove cookies and cool on racks.
To make frosting: In a large bowl, whisk together confectioners' sugar, milk, and cream. If mixture is too thick, add a little more milk (by the teaspoon until desired consistency is reached). Pour half of the frosting (about 3/4 cup) into another bowl and add vanilla and red food coloring until desired red color is reached.
Use an offset spatula to spread red frosting on half of the top of each cookie. Let stand until almost set, 20 minutes. Using a clean spatula, spread white frosting over unfrosted half of each cookie. (If the frosting thickens up during the process, whisk until loose.) Let set completely, about 1 hour.