1. Preheat the oven to 350°F to prepare for baking.
2. Grease the muffin tin or line it with cupcake liners to prevent sticking.
3. In a large bowl, mix the all-purpose flour, baking powder, and ground cinnamon, then set aside.
4. In a separate bowl, beat together the unsalted butter, granulated sugar, and brown sugar until light and fluffy.
5. Add the eggs one at a time to the butter-sugar mixture, mixing well after each addition.
6. Stir in the sour cream and vanilla extract until the mixture is smooth and creamy.
7. Gradually fold in the dry ingredients into the wet mixture, being careful not to overmix.
8. In another bowl, prepare the streusel topping by mixing brown sugar, granulated sugar, all-purpose flour, and ground cinnamon.
9. Add cold cubed butter to the streusel mixture and use a fork or pastry cutter to create a crumbly texture.
10. Spoon the muffin batter into the prepared tin, filling each cup halfway.
11. Add a tablespoon of the streusel topping over the batter in each cup.
12. Add another layer of batter to fill each cup three-quarters full.
13. Top with an additional layer of streusel, and swirl gently with a toothpick if desired.
14. Bake the muffins in the preheated oven for 15-25 minutes, or until a toothpick inserted in the center comes out clean.
15. Allow the muffins to cool in the tin for 5 minutes before transferring them to a wire rack to cool completely.