4. Add the Eggs and Vanilla:
Beat in the eggs, one at a time, making sure each is fully incorporated.
Stir in the vanilla extract.
5. Mix in the Dry Ingredients and Sour Cream:
Gradually add the dry ingredients to the wet ingredients, alternating with the sour cream. Start and end with the dry ingredients, mixing until just combined.
6. Fold in the Apples and Nuts:
Gently fold the diced apples and nuts (if using) into the batter until evenly distributed.
7. Transfer to the Pan:
Pour the batter into the prepared cake pan and spread it out evenly.
8. Make the Cinnamon Sugar Topping:
In a small bowl, mix together the sugar and cinnamon for the topping.
Sprinkle the cinnamon sugar mixture evenly over the top of the cake batter.
9. Bake the Cake:
Bake in the preheated oven for 40-45 minutes, or until a toothpick inserted into the center of the cake comes out clean or with just a few crumbs.
10. Cool and Serve:
Allow the cake to cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.
Serve as is, or dust with a little extra powdered sugar for garnish if desired.