Preheat the oven to 350°F (175°C).

Grease a 9x13 inch baking pan with butter or cooking spray.

In a large bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon.

In another bowl, beat together the softened butter and granulated sugar until light and fluffy.

Mix in the eggs, one at a time, then add the sour cream and vanilla extract.

Gradually add the dry ingredients to the wet mixture, stirring until just combined.

In a small bowl, combine the brown sugar, cinnamon, and chopped nuts for the topping.

Pour half of the batter into the prepared pan, sprinkle with the topping, then add the remaining batter on top.

Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean.

Let the cake cool in the pan for at least 10 minutes before serving.