For the Streusel Topping

1. In a medium bowl, add all purpose flour, granulated sugar, light brown sugar, cinnamon, salt, corn starch, and slightly cooled melted butter. Use a fork to rake the butter through the ingredients. Continue mixing until the mixture combines into formed crumbs and there are few pieces of the dry flour mixture.

For the Cinnamon Cookies

1. Preheat your oven to 350 degrees Fahrenheit and line baking sheets with parchment paper to ensure the cookies come off of the pan cleanly.
2. In a large bowl, combine slightly cooled melted unsalted butter, light brown sugar, granulated sugar, room temperature eggs, and pure vanilla extract together with a whisk until smooth and combined.
3. Add properly measured all purpose flour, baking soda, salt, and cinnamon to the bowl. Use a rubber spatula to combine the ingredients together until all of the dry ingredients are incorporated.
4. Roll the dough into 1 1/2 tablespoons (40g) balls of dough and place them at least 2 inches apart on your prepared baking sheets. Use your thumb to push down and create a wide well in the center of each dough ball.
5. Pack about 2 teaspoons of crumb topping into each well. Bake the cookies from 8-11 minutes or until the edges are light golden brown, crumb topping is golden brown, and the tops of the cookies look just slightly soft.
6. Sift powdered sugar over the tops of the cookies as desired. Allow the cookies to fully cool before storing tightly covered, in an airtight container, or individually wrapped at room temperature for up to 4 days or in the freezer for up to 4 months.