Step 1

Using a large bowl and electric mixer combine sour cream and butter until smooth and light in color. Add sugar, eggs, and extracts and mix until combined.

Step 2

In another bowl, whisk together; flour, corn starch, baking powder, baking soda, and salt. Add the dry mixture a little at a time to the wet ingredients and mix on low just until combined (don’t over-mix). Cover with plastic wrap and chill the dough in the refrigerator for 30 minutes to 1 hour.

Step 3

Preheat oven to 350°F and line baking sheets with parchment paper or a baking mat.

Step 4

After chilling, use a 2-tablespoon cookie scoop to portion out dough and roll into 2-inch balls (damp hands will help if the dough is sticky). Carefully drop onto prepared pans, leaving 2 ½ inches between each dough ball. Flatten cookies with a greased flat bottom of a glass (or just dip the bottom of the glass in water). Cookies should be about ¼-inch to ½-inch thick.

Step 5

Bake cookies in preheated oven until puffed and just lightly golden around the edges (they should be pretty pale in color) for about 8-10 minutes. Allow cookies to fully cool on the pan (they will continue to bake while cooling) before frosting.

Step 6

While the cookies cool, make the frosting. Using an electric mixer cream the butter then add the powdered sugar and vanilla and mix until well incorporated. Slowly add the 2 tablespoons of milk while mixing on low, then increase speed to high and mix until smooth. If the frosting seems too thick add just a little more milk until you reach desired consistency. Color frosting as desired with gel food coloring.

Step 7

Once cookies are completely cooled, frost and add sprinkles right away. Allow crusting buttercream to airdry for several hours or overnight before stacking or packaging.