Preheat oven to 425F. This high temperature is needed to achieve the signature puff of the Dutch baby.
In a large bowl, whisk eggs, flour, milk, sugar, and salt until smooth. the batter will be thin.
Place the skillet on the stovetop. Add the unsalted butter and melt it, swirling to coat the bottom and sides of the skillet.
Once the butter is melted, carefully transfer the skillet (including the melted butter) to the preheated oven. Let it heat for an additional 5 minutes. Be careful not to burn the butter.
Carefully remove the hot skillet from the oven using oven mitts. Immediately pour the batter into the preheated skillet with the melted butter. The butter will bubble around the edges.
Bake the Dutch baby for 12-15 minutes, or until the edges are golden brown and the center is puffed and almost set.
Remove the Dutch baby from the oven and serve it immediately while it's still puffed and fluffy. The center may sink a bit as it cools. That's normal. Add toppings like fresh fruit, caramel syrup, powdered sugar, maple syrup, whip cream and more!