Preheat the oven to 400 degrees F.

In a large, ovenproof skillet, melt 2 tablespoons of the butter over medium-high heat. Add the apples, sugar, cinnamon, and nutmeg, and cook, stirring, until the apples are soft and just golden, about 7 minutes. Add the walnuts, and cook, stirring, until the apples are caramelized, 2 to 3 minutes. Add the remaining tablespoon of butter and stir to melt. Remove from the heat.

In a large bowl, combine the eggs, milk, and baking powder, flour, and whisk just until blended, being careful not to over mix. Pour the batter over the apples. Bake until golden and puffed, 15 to 20 minutes.

Remove from the oven and sprinkle with powdered sugar. Drizzle with creme fraiche and maple syrup and serve in the pan.