Preheat your oven to 350°F (175°C). This ensures your cake bakes evenly.
Grease your Bundt pan generously with butter and dust it with flour, tapping out the excess.
In a large mixing bowl, beat the softened butter and 1 ¾ cups of the white sugar together using an electric mixer until light and fluffy (about 3-5 minutes).
Add the eggs one at a time, mixing well after each addition. Then, mix in the vanilla extract until combined.
In another bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt.
Gradually add the dry ingredients to the creamed mixture, alternating with the sour cream. Begin and end with the dry ingredients, mixing just until combined.
In a small bowl, combine the remaining ¼ cup of white sugar, ground cinnamon, and chopped walnuts. Gently fold this mixture into the cake batter.
Pour half of the batter into the prepared Bundt pan. Sprinkle half of the cinnamon-walnut mixture over the batter. Pour the remaining batter on top and finish with the last of the cinnamon-walnut mixture, swirling gently with a knife.
Bake in the preheated oven for 55-65 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for about 10 minutes before inverting it onto a wire rack to cool completely.