A Dutch baby, often called a German pancake, is similar to British Yorkshire pudding and American popovers. The batter, made with eggs, milk and flour, puffs up in the oven, forming the perfect canvas for sauteed bratwurst, onions and apple in this recipe. It's an ideal lunch or dinner for the cool weather, or a hearty breakfast.
Preheat the oven to 425 degrees F. Place a 10- or 12-inch cast-iron skillet in the oven to heat up for 10 minutes.
Meanwhile, in a large bowl, beat the eggs, milk, 1/2 cup of the flour, 3/4 teaspoon salt and 1/2 teaspoon pepper. Add the butter to the hot skillet and return it to the oven until the butter melts, about 2 minutes. Once the butter is melted, carefully pour the batter into the skillet and immediately return it to the oven. Bake until the Dutch baby is browned and puffed, 15 to 18 minutes.
Meanwhile, heat the olive oil in a large skillet over medium-high heat. Add the bratwurst and cook, stirring, until it is heated through and starts to brown, 3 to 5 minutes. Add the onion and apple and cook, stirring, until softened, 3 to 5 minutes. Add the remaining 1 tablespoon flour and cook, stirring, until the mixture is evenly coated, about 1 minute. Stir in the broth and simmer until the mixture is thickened, about 2 minutes. Stir in the mustard and season with salt and pepper.
Remove the Dutch baby from the oven. Spoon some of the bratwurst mixture on top and sprinkle with parsley. Serve right away, passing the remaining bratwurst mixture at the table.