Preparation

Position a rack in the center of the oven and heat the oven to 350°F (325°F if using a dark nonstick pan). Generously butter a 10-inch tube pan with a removable bottom.

Make the cake: In a medium bowl using an electric mixer on medium speed, cream together the margarine and sugar. Beat in the eggs one at a time, blending each one completely before adding the next.

In a separate bowl, sift together the flour, baking powder, baking soda, and salt.

On low speed, alternately add the dry ingredients and sour cream to the margarine mixture. Beat in the vanilla. Pour the batter into the prepared pan and spread evenly.

Sprinkle half of the cinnamon sugar on top of the batter, then swirl into the batter with the back of a spoon. Sprinkle the rest of the cinnamon sugar evenly over the top of the batter. Sprinkle walnuts on top of the batter.

Bake until the top of the cake is golden brown and a wooden skewer inserted into the center of the cake comes out clean, 50 to 55 minutes. Transfer to a wire rack and let cool for at least an hour before removing from the pan.