Preheat oven to 350℉. Line a baking sheet with parchment paper.

Combine the flour, brown sugar, and cinnamon in a bowl. Dot the dry ingredients with cubed, cold butter. Use a pastry blender to cut the butter into the ingredients until you have a sand like texture with a few larger lumps of butter.

Add the pecans and use your hands to combine everything. It should lump together a bit, but still be pretty sandy looking. Dump the streusel onto the baking sheet and gently pat it into a loose, even layer.

Bake for 15- 20 minutes. After 10 minutes, give the streusel a stir, then place it back in the oven. It will still be soft when it comes out, but it will firm up as it cools.

Once cool, transfer the streusel to an airtight container.

In a medium bowl, whisk together the flour, cornstarch, baking soda, and salt and set aside.

In a stand mixer, cream together the butter and both sugars on a low speed until combined. Scrape the bowl down once or twice as needed. Add the egg and vanilla and beat until combined. Scrape the bowl down as needed.

Place the trays in the freezer for at least one hour. Transfer the frozen cookie dough balls to a freezer bag or airtight container. Freeze for at least 4 hours, but preferably overnight.

When you are ready to bake, preheat the oven to 325°F. Place frozen cookie dough balls on a baking sheet lined with a silicone baking mat or parchment paper. Bake for 21- 23 minutes or until lightly golden brown.

Let them cool on the baking sheet for 5- 10 minutes before transferring them to a cooling rack.