Preheat the oven to 350 degrees F. Line the bottom of a 10-inch springform pan with parchment paper. Spray the sides with nonstick cooking spray.
Place the butter and sugar in the bowl of an electric stand mixer. Beat on high to cream the butter and sugar together until light and fluffy, 3-5 minutes.
In a separate bowl, mix the flour, baking powder, cinnamon, nutmeg, and salt.
Turn the mixer on low. Beat in the eggs and vanilla. Then alternate adding the flour mixture and sour cream, until both are combined in the batter.
Scrape the bowl with a spatula, then mix in the chopped walnuts. Scoop the batter into the prepared pan.
Peel the pear. Then core and slice into thin 1/16-inch wedges. Arrange the slices around the top of the cake in a flower pattern, tucking them into the batter just deep enough to hold them in place. Sprinkle 1 tablespoon sugar over the top of the cake.
Bake the cake undisturbed for 60 minutes. Check the center of the cake with a toothpick. If it comes out clean, remove from the oven. If not, bake another 5-10 minutes. Cool completely before releasing from the pan and cutting.
This cake can be made 2-3 days before serving. Cover and keep in the refrigerator, or on the countertop. Serve at room temperature.