Preheat oven to 350 degrees. Line 24 muffin cups with paper liners.For the streusel topping: In a small bowl, whisk together flour, brown sugar and cinnamon. Add in the butter and cut into the flour mixture using a pastry blender until crumbly.For the muffin batter: with a hand mixer, beat the butter and sugar together until fluffy. Add the eggs and beat until just combine. Add the vanilla.In a separate bowl whisk together the flour, baking powder and baking soda. Gradually add the flour mixture to the sugar mixture. Beat until just combined. Fold in the sour cream.Spoon half of the batter into the prepared muffin tins, sprinkle half of the streusel topping on top of the batter. Spoon remaining batter onto the streusel topping and sprinkle with the remaining streusel topping.Bake 18-20 minutes or until an inserted toothpick comes out clean. Cool for 10 minutes before enjoying.
