1. Preheat your oven to 350°F. Grease and flour a Bundt pan.

2. In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. In a large mixing bowl, cream the softened butter and granulated sugar until light and fluffy. Beat in the eggs, one at a time, followed by the vanilla extract. Mix in the sour cream until the batter is smooth. Gradually add the dry ingredients, mixing just until combined.

3. In a small bowl, combine the melted butter, brown sugar, cinnamon, and chopped nuts (if using).

4. Pour half of the cake batter into the prepared Bundt pan. Spoon the cinnamon swirl mixture evenly over the batter. Top with the remaining batter and gently swirl with a knife to create a marbled effect.

5. Bake the Cinnamon Swirl Bundt Cake for 50–60 minutes, or until a toothpick inserted into the center comes out clean. Allow the cake to cool in the pan for 10 minutes before inverting it onto a wire rack to cool completely.

6. If desired, whisk together the powdered sugar, milk, and vanilla extract until smooth. Drizzle the glaze over the cooled cake, allowing it to cascade down the sides for a stunning presentation.