Add the butter, brown sugar, and granulated sugar to a large mixing bowl (a stand mixer with a paddle attachment is my preferred, but a hand mixer works great too) and beat the mixture for 2 minutes until its light and creamy.
Add in the eggs and vanilla extract and stir until just combined.
Add in the flour, cornstarch, baking soda, baking powder and salt and stir them into the dry ingredients to make a nice soft cookie dough. Scrape the sides and bottom of the bowl as needed.
Measure out the dough to be 6 TBS (about 3.5oz) and separate that dough into 2 sections.
Press the bottom of a Tablespoon into one half of the dough to make and indent.
Then scoop out 2 tsp of the cinnamon filling and put it into the indent.
Use the other half of the dough to cover the cinnamon filling and pinch the dough together to seal it. Roll the dough into a tall ball.
Press the streusel crumbs evenly over the top and sides of the cookies, but not onto the bottom as it won't cook well there.
Place the cookie ball onto a baking sheet lined with parchment paper, repeat with additional cookie dough, filling, and streusel. And chill the cookie balls for at least 1 hour, up to overnight.
Preheat the oven to 375 degrees fahrenheit. Line a baking sheet with parchment paper.
Place 4 cookies on the prepared cookie sheet and bake until the edges are lightly golden sand the top looks barely set, and no longer gooey.
Remove the pan from the oven and let the cookies cool on the cookie sheet for 10 minutes. Then carefully transfer them to a cooling rack to cool more. Repeat baking the rest of the cookies.