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, stirring until completely combined.

Cover dough tightly with plastic wrap and refrigerate for 30-60 minutes.

While the dough chills, prepare the filling.

In a medium 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 and scoop by ¼ cup. Break and form one half into a nest.

Scoop a Tablespoon of the brown sugar filling into the nest.

Form the other half of the cookie dough into a flattened nest around the filling, sealing it inside.

Repeat until all dough and filling is used.

Place on baking sheet and freeze for 15-30 minutes. Preheat oven to 375F.

Bake for 14 minutes until edges are light 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 and allow to set before enjoying.