– 1 1/2 cups all-purpose flour – 1 cup granulated sugar – 1/2 cup unsalted butter, softened – 1/2 cup sour cream – 2 large egg – 1 teaspoon vanilla extract – 1 teaspoon baking powder – 1/2 teaspoon baking soda – 1/4 teaspoon salt – For the Streusel Topping:1/2 cup packed brown sugar 1/2 cup all-purpose flour 1 teaspoon ground cinnamon 4 tablespoons unsalted butter, melted

n a small bowl, mix together 1/2 cup packed brown sugar, 1/2 cup all-purpose flour, and 1 teaspoon ground cinnamon. Stir in 4 tablespoons of melted unsalted butter until the mixture resembles coarse crumbs. Set aside.

In a large bowl, cream together 1/2 cup softened unsalted butter and 1 cup granulated sugar until light and fluffy. Add 2 large eggs, one at a time, beating well after each addition. Stir in 1/2 cup sour cream and 1 teaspoon vanilla extract until smooth.

In a separate bowl, whisk together 1 1/2 cups all-purpose flour, 1 teaspoon baking powder, 1/2 teaspoon baking soda, and 1/4 teaspoon salt.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.

Preheat your oven to 350°F (175°C). Grease and flour a 9-inch square baking pan. Spread half of the cake batter into the prepared pan. Sprinkle half of the streusel topping evenly over the batter. Repeat with the remaining batter and streusel.