Combine flour, brown sugar, pinch of salt in a small bowl. Whisk together then pour in the melted butter. Place the bowl into the refrigerator.
In a separate bowl, combine brown sugar, flour, cinnamon, and melted butter. Mix until a thick paste forms. Set aside.
Combine room temperature, brown sugar, and white sugar the bowl of a stand mixer fitted with the paddle attachment. Cream together for 2 minutes, then add egg, egg yolk, and vanilla extract. Mix for 30 seconds, scrape down the sides of the bowl, then continue to mix on medium speed for an addition 1-2 minutes, until combined and fluffy.
Whisk together the dry ingredients in a large bowl - all purpose flour, baking soda, cinnamon, corn starch, and kosher salt. Add to the wet ingredients and mix until just combined, about 30 seconds.
Use a large cookie scoop to scoop cookie dough. Roll into a ball, then press the center of the cookie to form a well in middle. Add about 1 tbsp of the cinnamon streusel. Remove the crunchy streusel from the refrigerator and sprinkle on top of the cookie, enough to cover the cinnamon filling. Repeat with the remaining cookies and place onto a cookie sheet lined with parchment paper. Refrigerate uncovered for 30 minutes.
Preheat the oven to 350 degrees F. Bake 5 cookies at a time, spacing them out about 2 inches apart. Bake for 12-14 minutes. Immediately out of the oven, use the opening of a cup to "swivel" around the cookie to create a perfect circle shape. Allow the cookies to cool on the baking sheet for 10 minutes, then remove onto a wire rack to cool completely. Dust with powdered sugar!