Preheat your oven to 350°F (175°C) and grease and flour a 10-inch Bundt pan.

In a medium bowl, whisk together 2 cups of flour, 1.5 teaspoons of baking powder, 0.5 teaspoon of baking soda, and 0.5 teaspoon of salt.

In a large bowl, cream together 0.5 cups softened butter and 1 cup granulated sugar until light and fluffy, about 3-5 minutes.

Add 2 large eggs, one at a time, mixing well after each addition, then stir in 2 teaspoons of vanilla extract.

Gradually add the dry mixture to the wet ingredients, alternating with 0.5 cups of sour cream, stirring until just combined.

In a separate bowl, mix together 0.5 cups melted butter, 0.5 cups light brown sugar, and 1 tablespoon ground cinnamon. Fold in chopped nuts if desired.

Spoon half of the cake batter into the prepared Bundt pan, layer with half of the cinnamon mixture, then add the remaining batter and top with the rest of the cinnamon.

Gently swirl the cinnamon mixture into the batter for a marbled effect.

Bake for 50-60 minutes until a toothpick inserted comes out clean.

Let the cake cool in the pan for 10-15 minutes then invert onto a wire rack to cool completely.

Whisk together 1 cup of powdered sugar, 2 tablespoons of milk, and a splash of vanilla for the glaze and drizzle over the cooled cake.