In a medium bowl, combine 1/2 cup flour, 1/3 cup brown sugar, 2 tsp cinnamon, and pinch of salt. Work in 5 Tbsp softened butter with your fingers until small clumps form. Refrigerate while preparing cookie dough.

Preheat oven to 400°F. Line two baking sheets with parchment paper or silicone baking mats.

In a large bowl, whisk together 1 1/4 cup all-purpose flour, 3/4 cup cake flour, 1 tsp cornstarch, 1 tsp cinnamon, 1/2 tsp baking soda, 1/2 tsp baking powder, and 1/2 tsp salt. Set aside.

In stand mixer with paddle attachment, cream 8 Tbsp cold cubed butter with 1/2 cup brown sugar and 1/4 cup granulated sugar until smooth, about 1-2 minutes.

Add 1 egg, 1 egg yolk, and 1 tsp vanilla extract. Blend until mixed, scraping down sides of bowl as needed.

Gradually add dry ingredients about 1/4 cup at a time, mixing until just incorporated.

Scoop and roll dough into 8 large balls (or 22-24 smaller cookies). Place on prepared baking sheets.

Make an indent in each cookie using your thumb or the floured end of a spoon. Spoon about 1 Tbsp of streusel filling into each indent.

Bake for 8-11 minutes, or until edges appear set and slightly golden. Remove just before they look completely done to prevent over-baking.

Optional: Immediately after removing from oven, use a circular cookie cutter or glass (larger than the cookie) to spin cookies into perfect circles.

Let cookies rest on baking sheet for 5 minutes, then transfer to cooling rack.

For icing, whisk together 2 Tbsp melted butter, 3 Tbsp heavy cream, 1 cup sifted powdered sugar, 1 tsp vanilla, and pinch of salt. Once cookies are completely cool, drizzle icing over tops.