In a blender, combine the sugar, vanilla, eggs, flour, milk, and salt and blend until smooth.
In a large, oven safe skillet, melt 1 tablespoon of the butter. Once melted, add in the apple slices, BROWN sugar, cinnamon and nutmeg. Stir to combine. Saute the apples for 5 minutes, stirring often, until they just begin to soften. Remove to a bowl and don't bother to wipe clean the skillet (we want the apples and sugar mixture to still be in there!).
Add the remaining 2 tablespoons of butter to the skillet and place the skillet in the pre-heated oven until the butter is melted; about 2-4 minutes.
Remove from the oven and quickly arrange the apples. You can simply dump the apples in and distribute them evenly around the skillet OR you can arrange them in a circle like I did. Drizzle on any of the liquid that remains (see video for reference).
Gently pour the batter over top of the apples and put directly into the oven. Bake for 20-25 minutes until it’s puffed up around the edges and browned all over.