Preheat oven to 430F. (non-convection setting). Place 3 creme brûlée ramekins onto a baking sheet and set aside. *See Note 1 below.
In a large bowl, whisk together the flour and cornstarch. In another bowl or a measuring cup, whisk together the milk, eggs, sugar, melted butter, vanilla and salt. Add about 1/3 of the egg mixture to the flour mixture and whisk together until it is a smooth paste, then slowly whisk in the remaining egg mixture. Let the batter rest while you prepare the maple apples.
In a skillet, melt the 2 Tablespoons butter for the maple apples over medium heat. Add the prepared apple slices, then add the brown sugar, maple syrup and cinnamon. Stir together to coat the apples. Cook over medium heat, stirring regularly, until the apples are softened and the sauce is syrupy. Remove from the heat and set aside.
When the oven is preheated, divide the 1 1/2 Tablespoons of butter between the 3 ramekins. Pop the ramekins into the oven on the baking sheet for about 2 minutes, or until the butter is completely melted.
Remove the baking sheet from the oven. Briefly stir the batter, then immediately pour into the hot ramekins, dividing equally between them. The batter should only fill the ramekins about 1/3 full.
Immediately place into the oven on the baking sheet and bake for 12-15 minutes, or until puffed and golden.
When the Dutch babies are almost cooked, return the skillet with the apples to a burner to warm over medium-low heat.
Remove from the oven. The Dutch baby pancakes will quickly deflate and leave a cavity in the centre. Spoon the warm maple apples into the cavity, dividing between the 3 ramekins.
Serve immediately sprinkled with chopped walnuts or pecans and dusted with icing sugar. If you like, add a dollop of creme fraiche or for dessert, add a scoop of vanilla ice cream.
Notes
Note 1: If you have the wider, round and shallow ramekins (aka creme brulee ramekins), as shown here, those are ideal as they provide a nice centre space to spoon in the maple apples. Alternatively, you can use a smaller, taller ramekin. You may get an extra serving with smaller ramekins. Be sure not to fill the ramekins more than about 1/3 full, as they will puff up considerably as they bake!Be sure to read the notes above this Recipe Card, for more tips on making this recipe. You'll also find step-by-step photos there, that you may find helpful.