Preheat oven to 375°F (190°C) and line a 12-cup muffin tin with paper liners. In a bowl, whisk together the 2 cups flour, baking powder, baking soda, salt, and 1 teaspoon cinnamon. Set aside.

In a large bowl, beat the ½ cup butter and ¾ cup sugar until light and fluffy. Add eggs one at a time, then mix in sour cream and vanilla. The mixture will look curdled.

Fold dry ingredients into the wet in two additions, just until combined. Do not overmix.

Spoon about 1 tablespoon of batter into each liner, spread it, and sprinkle with half of the cinnamon sugar mixture (the ¼ cup sugar and 1 teaspoon cinnamon). Top with remaining batter and sprinkle with the rest of the cinnamon sugar.

To make the streusel, combine ½ cup flour, brown sugar, and 1 teaspoon cinnamon. Cut in cold butter until crumbly. Sprinkle over muffins and bake 18 to 22 minutes, until golden and a toothpick comes out clean.

Cool in the pan for 5 minutes, then transfer to a wire rack. Serve warm.