Combine the flour, salt, baking powder, baking soda, and cornstarch in a bowl then whisk together and set aside.

Cream the butter and sugar until fluffy then beat in the egg, vanilla, and almond extract if using.

Add the sour cream and mix until combined, scraping the bowl down as needed.

Add the dry mixture to the wet and mix on low until just combined. Use a spatula to scrape down the bowl and combine any errant flour.

Shape dough into a disk, cover in plastic, and chill for 1 hour.

Preheat oven to 375°F.

Roll the dough out to 1/4 inch thickness and use a 2 1/2-3 inch circular cookie cutter to cut the cookies. Reroll scraps and cut remaining cookies.

Transfer cookies to parchment-lined baking sheets and bake at 375°F for 8-9 minutes or until the cookies are just turning color on the bottom edge. Set aside to cool completely.

While the cookies bake, cream the butter then mix in the powdered sugar and vanilla.

Drizzle in the milk while mixing on low, then increase speed to high and beat until smooth. If using food dye, mix in a drop at a time until desired color is reached.

Top the cookies with a thin layer of buttercream and a smattering of sprinkles.