Preheat oven to 350°F. Grease a 9x13 baking pan.
Make streusel: mix brown sugar, flour, and cinnamon. Cut in cold butter until crumbly. Set aside.
Whisk flour, sugar, baking powder, salt, and cinnamon in a large bowl.
In a separate bowl, whisk eggs, sour cream, melted butter, and vanilla. Fold into dry ingredients until just combined.
Spread batter into the prepared pan. Sprinkle streusel evenly over the top.
Bake for 30 to 35 minutes until a toothpick comes out clean. Cool before cutting into squares.