
Preheat oven to 350F (177C) and line baking sheets with parchment paper. Set aside.
In a large mixing bowl, use an electric mixer to mix together butter and sugar until light and fluffy.
Add egg, egg yolk, sour cream, vanilla extract, and almond extract and stir well until completely combined.
In a separate, medium sized bowl whisk together flour, cornstarch, baking powder, baking soda, and salt.
Gradually add dry ingredients to the wet, stirring on low speed until all ingredients are well combined.
Drop cookie dough by 2-Tablespoon (40g) sized scoop onto the prepared baking sheet, spacing cookies at least 2 inches (5cm) apart. If desired, you can gently roll the dough between your palms to make it smooth (for more uniform cookies), but it is a bit sticky.
Transfer to center rack of 350F (175C) preheated oven and bake for 10-11 minutes.
Immediately after removing from the oven, lightly flatten each cookie by gently pressing down on them with a flat surface, such as the bottom of a large measuring cup. Allow to cool completely before frosting.
In a medium sized mixing bowl, use your electric mixer to beat butter until smooth and creamy.
Gradually add powdered sugar, mixing on low speed, until sugar is completely combined.
Add vanilla and salt, stir to combine.
Add food coloring, if using, and stir until color is even throughout.
When cookies are completely cooled, spread frosting evenly over cookies. Decorate with sprinkles, if desired.