In a small bowl, mix together the sugar and cinnamon.
Make the batter
Preheat the oven to 375°F. Butter a 9 by 5-inch standard loaf pan.
In a large bowl, using an electric mixer at medium speed, beat the eggs until frothy, about 3 minutes. Add the sugar and vanilla, beating until smooth. In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.
Add the melted butter and the sour cream to the egg-and-sugar mixture; beat until well combined. At low speed, add the dry mixture to the wet mixture a spoonful at a time, beating just until smooth. Fold in the chocolate chips.
Spread half of the batter in the prepared pan and sprinkle evenly with about two-thirds of the cinnamon sugar. Sprinkle with the walnuts. Top with the remaining batter, spreading evenly. (This cake rises considerably, so be sure the batter is at least ¾ inch below the rim of the pan.) Sprinkle with the remaining cinnamon sugar.
Bake for 45 to 50 minutes or until a knife or skewer inserted in the center comes out clean.