Preheat the oven to 425.
Peel, core, and thinly slice two apples of your choice.
Toss with lemon juice, cinnamon, and sugar.
Melt butter in a 10-inch skillet (preferably cast iron).
Turn off heat.
Remove 2 tbsp. of the melted butter and pour into a mixing bowl.
Combine butter with eggs, milk, vanilla, flour, and salt. Set aside.
Put skillet back on burner, add sliced apple mixture to pan and cook until the apples are sizzling and slightly cooked (they should still hold their shape) for just a few minutes.
Pour the batter on top of the apples, sprinkle the top with brown sugar and put it in the preheated oven.
Bake until golden and puffy, about 20 to 25 minutes.
Dust with a little confectioners' sugar and serve immediately.