To make the streusel topping, mix flour, brown sugar, cinnamon, and salt in a medium bowl. Use your fingers to blend in the cold butter until small clumps appear. Cover and chill.

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

In a large bowl, whisk together all-purpose flour, cake flour, cornstarch, cinnamon, baking soda, baking powder, and salt.

In a stand mixer, cream together the cubed butter and both sugars for about 1-2 minutes until smooth.

Beat in the egg, egg yolk, and vanilla extract until combined. Scrape down the bowl and mix again.

Gradually add the dry ingredients, mixing about 1/4 cup at a time until everything is well incorporated.

Scoop and roll the cookie dough into about 8 large balls or smaller if desired, placing them on the prepared sheets.

Use your thumb or the back of a spoon to press an indent into each ball.

Fill each cookie with approximately 1 Tbsp. of the streusel mixture. Bake for around 9-11 minutes, or until the edges are barely set and lightly golden.

For perfectly round cookies, right after baking, use a circular cutter to gently shape them if needed.

Allow cookies to cool on the sheet for around 5 minutes before transferring them to a wire rack.

Mix together the icing ingredients and drizzle over the cooled cookies. Enjoy your sweet treat!