1. Preheat the oven to 325º. Grease and lightly flour a 9- to 10-inch bundt pan.
2. Make the cinnamon-sugar mixture: Combine the cinnamon and sugar in a small bowl and set aside.
3. Make the candy mixture: Place the candy bars in a large zip-close bag, seal, then use a rolling pin to smash the candybars into small, bite-size pieces. Add the nuts to the bag, shake to mix, and set aside.
4. Make the cake batter: Sift the flour, baking powder, baking soda, and salt into a large bowl. Add the butter and, using an electric mixer or a spoon, mix well to incorporate. Add the sugar, eggs, and sour cream; blend well.
5. In a small skillet, melt the butter for the crumble and set aside.
6. Spoon half of the batter into the prepared pan. Sprinkle with half of the cinnamon sugar and half of the candy mixture. Top with the remaining batter, then sprinkle with the remaining cinnamon- sugar and candy mixtures. Top with the melted butter.
7. Bake the cake on the middle shelf of the oven for 45 to 55 minutes, or until a toothpick inserted in the center comes out clean. Let the cake cool completely in the pan, then use a flat knife or flat spatula to gently loosen it from the pan. Remove and place on a serving plate.