For the Apple Topping:
Preheat the oven to 350 degrees F or 175 degrees C.
In a small bowl, combine the butter, brown sugar, cinnamon, nutmeg and salt and stir until a smooth paste forms.
Spread evenly over the bottom of an 8-inch round cake pan sprayed with gluten free nonstick cooking spray.
Top this mixture with the apple slices arranged in a pattern you’d like.
Sprinkle the chopped walnuts over the apple slices and set aside while you make the cake batter.
For the Cake Batter:
In a large mixing bowl, whisk together the melted butter, milk, applesauce, eggs, brown sugar and cinnamon until everything is well combined.
Add the gluten free Bisquick to this mixture and stir until everything is well combined and lump free. You’ll notice that the batter has a much denser consistency than most cake batters.
Spoon the batter over the apple walnut mixture being careful not to disturb the apples as you smooth the batter into place with either a rubber spatula or the back of a spoon.
Bake the cake on the middle rack of your oven preheated at 350 degrees F for 40 to 45 minutes or until a toothpick inserted comes out clean.
Let it cool for five minutes before inverting it onto your serving dish. If any apples remain in your pan simply place them back where they belong. Let the cake cool for at least 1 hour before serving.
Got a sweet tooth? Here's a totally sinful dessert recipe that you should not miss. Watch this video to learn a detailed method of how you an prepare this luscious Walnut Upside Down Cake with Apple Topping.