Combine butter and sugars in a large mixing bowl and use an electric mixer to beat until light, fluffy, and well-creamed.

Add eggs and vanilla extract and stir again until thoroughly combined. Set aside.

In a separate bowl, whisk together flour, cornstarch, baking powder, baking soda, and salt.

Gradually add dry ingredients to wet (in 4 or 5 parts) stirring until completely combined.

Cover dough tightly with plastic wrap and transfer to the refrigerator to chill for 30-60 minutes.

While the dough chills, prepare the filling.

In a medium mixing bowl, combine butter, sugar, and vanilla and stir until smooth and creamy.

Sprinkle flour, cinnamon, and salt over the mixture and stir until well combined.

Remove chilled cookie dough from the refrigerator and scoop by ¼ cup. Break the scoop in half and form one half into a nest. Add a tablespoon of filling and seal with the other half of dough.

Place cookie dough on a baking sheet and place in the freezer for 15-30 minutes.

Preheat oven to 375F (190C) and line a baking sheet with parchment paper.

Bake for 14 minutes, until the edges are lightly golden brown. Cool completely before icing.

In a small bowl, combine powdered sugar, brown sugar, milk, corn syrup, vanilla extract, and cinnamon. Whisk until smooth.

Drizzle over cooled cookies. Allow to set before enjoying.