Preheat the oven to 350 degrees Fahrenheit and line two baking sheets with parchment paper.
Cream the softened butter, brown sugar, and white sugar in a bowl until light and fluffy. Mix in the egg and vanilla extract.
Whisk together the flour, baking powder, cinnamon, and salt in a separate bowl. Slowly fold these dry ingredients into the wet dough until just combined.
Prepare the streusel by cutting the cold cubed butter into the streusel flour, brown sugar, and cinnamon using a pastry cutter until crumbly.
Scoop two tablespoons of cookie dough per cookie onto the pans, flatten slightly, and press the streusel into the tops of the dough.
Bake for 11 to 13 minutes until edges are golden. Let cool on the pan for 5 minutes before moving to a wire rack.
