• Using a countertop mixer, cream together the butter and sugar until light and fluffy (2-3 minutes on medium speed). Add the eggs, egg yolk, sour cream and vanilla. Mix just until blended.
• In a separate bowl, combine the dry ingredients (baking soda, baking powder and flour) until well combined.
• Add half of the dry ingredients to the bowl; mix just until combined. Repeat with the remaining dry ingredients.
• Refrigerate dough for 3 hours.
• Preheat oven to 425°F.
• Line 2 baking sheets with parchment paper; set aside.
• Roll dough out on a well-floured countertop to 1/4" thickness. Use a cookie cutter to cut desired shapes. Place cookies on lined baking sheets.
• Bake cookies for 9-10 minutes, or until edges turn light golden brown. Place cookies on a cooling rack until fully cooled.

For the Frosting

• Using a countertop mixer, beat together the powdered sugar and melted butter until well combined.
• Add the milk and vanilla; beat until combined. (Note: If the frosting is too thin, add an extra ¼ cup of powdered sugar. If it is too thick, add an extra tsp of milk.)
• Gradually add the red food coloring until frosting reaches desired color.
• Frost and decorate cookies.