Using a countertop mixer, cream the butter, sugar and brown together until light and fluffy (~2-3 minutes on medium speed).

Add maple syrup, egg, egg yolks and vanilla; mix on low speed until well combined.

Add flour, baking powder and salt; mix on low speed until well combined.

Roll dough into large ball and wrap with plastic wrap. Refrigerate for at least 60 minutes.

Preheat oven to 375°F.

On a well-floured countertop, roll dough to ¼” thickness. Using a 3” round cookie cutter, cut dough into circles. Place circles on parchment-lined baking sheet at least 1” apart.

Bake for 15-18 minutes or until edges of cookies just begin to turn brown.

Let cookies cool completely before removing from pan.

Using a medium mixing bowl, whisk together all frosting ingredients until smooth. (Note: If the frosting is too thin, add an extra ¼ cup of powdered sugar. If it is too thick, add 1 tsp of milk.)

Frost the cookies.

{Optional} Before frosting sets, sprinkle tops of cookies with fall-themed sprinkles.