For the Dutch baby: Place an ovenproof 12-inch skillet in the oven and preheat to 425 degrees F.
In a blender, combine the flour, eggs, milk, sugar, vanilla and salt. Blend on high to make a smooth batter. Let the batter rest while the oven heats up.
Once the oven is preheated, carefully remove the skillet and add the butter. Let the butter melt and sizzle, then pour in the batter. Return the skillet to the oven.
Bake the Dutch baby until the edges are puffed and browned and the middle is set, 20 to 25 minutes.
For the blueberry-orange compote: Meanwhile, zest the orange into a small skillet; squeeze the juice from half of the orange into the skillet. Add the granulated sugar, nutmeg and blueberries. Bring to a simmer over medium-high heat. Cook, swirling the skillet, until the sauce is thick and syrupy and the berries are beginning to soften, 3 to 5 minutes. Remove from the heat and stir in the butter. Keep warm.
Serve the Dutch baby hot, topped with the compote and dusted with confectioners' sugar if desired.