Prepare the cookie dough

Combine butter and sugars in a large mixing bowl and use an electric mixer (or stand mixer fitted with paddle attachment) to beat until light, fluffy, and well-creamed).

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

In a separate, medium-sized mixing 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 (note I do not recommend chilling longer than this, as the dough becomes difficult to manage).

While the dough chills, prepare the filling.

For the filling

In a medium-sized mixing bowl, combine butter, sugar, and vanilla and stir or beat with an electric mixer until smooth and creamy.

Sprinkle flour, cinnamon, and salt over the butter/sugar mixture and stir until well-combined.

Assembly

Remove chilled cookie dough from the refrigerator and scoop by ¼ cup (3 oz/85g). Break the scoop in half and form one half into a nest. Firmly scoop a Tablespoon of the brown sugar filling and scoop into the nest you just made in the center of the cookie dough. Take the other half of the cookie dough, likewise form it into a flattened nest shape and form it around the top of the filling to seal the filling inside in the center (I show how to do this in the video). Make sure the filling is completely concealed and centered. Repeat until all cookie dough and filling is used.

Place cookie dough on large plate or baking sheet and place in the freezer for 15-30 minutes (see note to chill longer, this dough freezes well). (note: you may chill this cookie dough longer, for days or even weeks, just make sure to transfer the dough to an airtight container (and if I’m chilling longer than a week I individually wrap each cookie dough ball in plastic wrap before freezing). Meanwhile, preheat your oven to 375F (190C) and line a baking sheet with parchment paper. .

Once cookie dough has chilled and oven is preheated, remove from freezer and place on parchment paper lined baking sheet, spacing cookies at least 2” apart (I only bake 4-6 cookies at a time). Transfer to center rack of 375F (190C) and bake for 14 minutes, until the very edges of the cookies are just beginning to turn a light golden brown. Remove from oven and allow to cool completely on baking sheet (cookies are fragile when warm!) before icing.

For the Icing

In a small bowl, combine powdered sugar, brown sugar, 1 Tablespoon of milk, corn syrup, vanilla extract and cinnamon. Whisk until smooth, adding additional milk as needed until mixture is smooth and ribbons off the whisk (the ribbon that falls should hold its shape for several seconds before dissolving back into the bowl, any thinner and it will take painfully long for your icing to set on the cookies!).

Immediately drizzle over cooled cookies. Allow to set before enjoying (note it could take up to several hours for the icing to harden completely, depending on how thin/thick your icing is).