Preheat the Oven: Preheat your oven to 350°F (175°C). Grease a 9-inch springform pan or a regular cake pan and line the bottom with parchment paper for easy removal.

Make the Streusel:

• In a medium bowl, combine 1 cup flour, ⅓ cup granulated sugar, ⅓ cup brown sugar, 2 teaspoons cinnamon, and ⅛ teaspoon salt.

• Pour in 6 tablespoons of melted butter and mix until the mixture resembles coarse crumbs. Set aside.

Prepare the Cake Batter:

• In a medium bowl, whisk together 1 ¾ cups flour, 1 ¼ teaspoons baking powder, ¼ teaspoon baking soda, and ¼ teaspoon salt. Set aside.

• In a large mixing bowl, beat ½ cup softened butter and 1 cup granulated sugar together until light and fluffy, about 2-3 minutes.

• Add 2 eggs, one at a time, beating well after each addition. Mix in 1 ½ teaspoons vanilla extract.

• Gradually add the dry ingredients to the wet ingredients, alternating with 1 cup sour cream. Begin and end with the dry ingredients. Mix until just combined; do not overmix.

Assemble the Cake:

• Spread half of the cake batter evenly into the prepared pan.

• Sprinkle half of the streusel mixture over the batter.

• Carefully spread the remaining batter over the streusel layer. Use a spatula to smooth the top.

• Sprinkle the remaining streusel evenly over the top.

Bake the Cake:

• Bake in the preheated oven for 45-55 minutes, or until a toothpick inserted into the center comes out clean.

• If the streusel starts to brown too quickly, cover the cake loosely with aluminum foil.

Cool and Serve:

• Allow the cake to cool in the pan for 15-20 minutes before removing it from the pan.

• Transfer to a wire rack to cool completely. Slice and serve.