Preheat the oven:
Arrange a rack in the middle of the oven and remove any racks above it. Place a standard 12-well muffin pan on the rack and preheat the oven to 425ºF (220°C).
Prepare the batter:
In a blender or food processor fitted with the blade attachment, combine the flour, milk, eggs, sugar, vanilla extract, and salt. Blend for 1 minute until smooth and liquidy. Let the batter rest in the blender for 10 minutes.
Prep the muffin pan:
While the batter is resting, cut the butter into 12 pieces. When the oven is preheated, carefully remove the hot muffin pan and place 1 piece of butter in each well.
Pour the batter:
Pour the rested batter into the buttered muffin wells, about 1/3 cup per well. Don’t worry if the butter hasn’t completely melted yet.
Bake:
Bake for 12-15 minutes or until the mini Dutch babies are puffed and golden brown.
Serve:
Let the Dutch babies cool for 1 minute before dusting them with powdered sugar or filling them with jam. Serve warm and enjoy!