First, make the cinnamon streusel. In a medium bowl, combine flour, brown sugar, cinnamon, and butter. Mix together with your hands or a fork, until you have a crumbly mixture. Set aside.
In a large bowl, whisk together flour, sugar, baking powder, soda, and salt. In a small bowl, whisk together buttermilk, eggs, oil, and vanilla. Add wet ingredients to the flour mixture and stir just until combined. Do not over mix, batter will be slightly lumpy.
Heat a griddle or pan to medium low. Coat with cooking spray. Drop 1 cup of batter onto heated skillet. Add 2 tablespoons of the cinnamon streusel. Cook on the first side until bubbles begin to form, about 2-3 minutes. Carefully flip pancake over and cover very generously with cinnamon streusel. Cook for another 2-3 minutes or until golden brown. Continue this process to make the rest of the pancakes.
Serve warm with maple syrup and butter.