Preheat oven to 350 degrees. I use convection setting. Lightly spray 9" round cake pan.
For caramel sauce, combine butter, sugar, cinnamon, and nutmeg in small saucepan. Heat to boiling, stir constantly. Remove from heat as soon as boil is reached.
Scrape caramel mixture into prepared pan. Arrange pear slices over caramel.
For cake batter, beat butter and sugar about 1 minute. Add eggs and vanilla, beat until fluffy, about 2 minutes. Sprinkle in dry ingredients and beat about 10 seconds. Pour in milk and beat until evenly moistened, about 1 minute. Pour over pears.
Carefully lift pan and bang pan on counter twice to release air bubbles.
Bake 45 minutes. Check with knife. When done run knife around edges to loosen. Place plate over and flip onto plate.