Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13 inch baking pan.

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.

In a large bowl, cream together the butter and sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla.

In a separate bowl, combine the sour cream.

Gradually add the dry ingredients to the wet ingredients, alternating with the sour cream, beginning and ending with the dry ingredients. Mix until just combined.

In a small bowl, combine the sugar and cinnamon for the filling. If using, stir in the chopped nuts.

Pour half of the cake batter into the prepared pan. Sprinkle with half of the cinnamon-sugar filling.

Top with the remaining cake batter, then sprinkle with the remaining cinnamon-sugar filling.

Bake for 40-45 minutes, or until a wooden skewer inserted into the center comes out clean.

Let cool in the pan for 10 minutes before inverting onto a wire rack to cool completely.

In a small bowl, whisk together the powdered sugar, milk (or cream), and vanilla extract until smooth.

Drizzle the glaze over the cooled cake.