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 mixing bowl, whisk together flour, cornstarch, baking powder, baking soda, and salt.

Gradually add dry ingredients to wet, stirring until completely combined.

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

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

Sprinkle flour, cinnamon, and salt over the butter/sugar 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.

Scoop a tablespoon of the brown sugar filling into the nest you made. Take the other half of the cookie dough and form it into a flattened nest shape around the filling.

Repeat until all cookie dough and filling is used.

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

Preheat oven to 375F (190C). Once cookie dough has chilled, place on the prepared baking sheet, spacing cookies 2 inches apart. Bake for 14 minutes.

Allow to cool completely on baking sheet before icing.

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

Immediately drizzle over cooled cookies and allow to set before enjoying.