Preheat the oven to 350 degrees. Grease and flour a 9x9 baking pan and set aside.
Beat the butter and brown sugar in a large mixing bowl for 2 to 3 minutes until well combined. The butter and brown sugar will have an appearance similar to grainy melted caramel. Beat in the vanilla and eggs until light and creamy. Add the pumpkin and beat until combined.
In a separate bowl, combine the flour, baking powder, soda, salt, and spices. Beat the dry ingredients into the wet ingredients on low speed of mixer. Remove mixer from bowl and stir in the pecans.
Spread the batter in the prepared pan.
Add all ingredients for the cream cheese batter to a medium bowl and mix on medium speed until smooth. Spoon dollops of the cream cheese onto the pumpkin batter. Lightly swirl the two batters together with a table knife. Sprinkle the top with remaining pecans.
Bake for 30 to 35 minutes or until a tester inserted near the center comes out clean.
Cool completely. Slice and serve. Sprinkle with powdered sugar if desired.