Preheat your oven to 350°F (175°C). Grease and flour a 9x13-inch baking pan.
In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.
Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract and sour cream until combined.
In a separate bowl, whisk together the flour, baking powder, baking soda, and salt.
Gradually add the dry ingredients to the wet mixture, stirring until just combined. Do not overmix; it’s okay if there are a few lumps.
In a small bowl, mix together the ground cinnamon, brown sugar, and chopped nuts (if using). This will be your streusel topping.
Pour half of the batter into the prepared baking pan and spread it evenly. Sprinkle half of the streusel mixture on top.
Pour the remaining batter over the streusel layer and spread gently. Finally, sprinkle the remaining streusel mixture on top.
Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center of the cake comes out clean.
Allow the cake to cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.
Notes
Serve the cake warm or at room temperature, dusted lightly with powdered sugar for an elegant touch. Pair with a hot cup of coffee for the perfect afternoon treat!