In a large bowl, whisk together flour, cornstarch, baking powder, baking soda, salt, and cream of tartar. Set aside.
2¼ cups cake flour, 2 tablespoons cornstarch, ½ teaspoon baking powder, ½ teaspoon baking soda, ½ teaspoon kosher salt, ¼ teaspoon cream of tartar
In another large bowl, using a hand mixer, beat the butter, cream cheese, and sugar together until light and fluffy, about 2 minutes. Add the egg, milk, vanilla, and almond extract and mix until well combined, about 1 minute.
½ cup unsalted butter, 4 ounces cream cheese, 1 cup granulated sugar, 1 large egg, 1 tablespoon milk, 1 teaspoon pure vanilla extract, ½ teaspoon almond extract
Add the dry ingredients into the wet and beat until just combined, about 30 seconds. Cover the bowl with plastic wrap and chill for 1 hour, up to overnight.
When ready to bake, preheat the oven to 325°F, and line 2 baking sheets with parchment paper.
Use a heaping 1-ounce cookie scoop to portion the dough. Roll into balls and place 2 inches apart onto the baking sheet. Flatten the top of the balls gently with your palm.
Bake until edges are just set, but centers are still slightly underdone, 11-13 minutes. Cookies shouldn’t gain much color on top. Let cool completely on baking sheets.
While the cookies cool, make the frosting: In a large bowl, using a hand mixer, beat the butter until completely smooth and creamy, about 2 minutes. Add the powdered sugar and beat again until light and fluffy, about 3 minutes more. Add the heavy cream, vanilla, and salt and beat until combined. If you’d like, add food coloring and beat again to combine.
2½ cups powdered sugar, 2 tablespoons heavy cream, 1 teaspoon pure vanilla extract, ⅛ teaspoon kosher salt, Food coloring, ¾ cup unsalted butter
Use an offset spatula or spoon to frost the tops of the cooled cookies with a thick amount of frosting and top with sprinkles, if desired.
Sprinkles