01 -
Preheat oven to 350°F (175°C). Grease a Bundt pan thoroughly, ensuring all crevices are coated to prevent sticking.
02 -
In a large bowl, beat together the unsalted butter and granulated sugar until pale and fluffy using a mixer on medium speed.
03 -
Add eggs to the creamed mixture one at a time, mixing well after each addition. Blend in vanilla extract until fully combined.
04 -
In a separate bowl, whisk together all-purpose flour, baking soda, and baking powder until uniformly mixed.
05 -
Add dry ingredients to the butter mixture in three batches, alternating with sour cream and mixing until just combined after each addition. Fold in chopped walnuts if using.
06 -
Spoon half of the batter into the prepared Bundt pan. In a small bowl, blend granulated sugar with ground cinnamon. Sprinkle the cinnamon sugar evenly over the batter. Top with remaining batter and gently swirl with a flat-blade knife.
07 -
Bake in preheated oven for 45 to 50 minutes or until a toothpick inserted into the center comes out clean.
08 -
Allow cake to cool in the pan for 10 minutes. Invert onto a wire rack and let cool completely before slicing.