3 tablespoons butter
1/2 cup flour
1/2 cup milk
Pinch (1/8 teaspoon or less) salt
Cut butter into a cast iron skillet. Heat the skillet in a 400F oven until it melts. While it's melting, mix the rest of the ingredients until combined. Pull the skillet out of the oven, pour the batter in evenly, and return to the oven. Bake until puffy and browned, about 15 to 20 minutes.
For extra super deliciousness, sprinkle lightly with powdered sugar while still hot and top with some fresh raspberries or blackberries. Strawberries would be good too! Goes great for a sunny lazy Sunday breakfast with fresh squeezed juice.
Personal Note: My parents used to make Yorkshire pudding every Christmas because they always made a huge roast beef, so the drippings were handy, and because my otherwise Spartan and health-conscious maternal grandmother inhaled the stuff. I'd never heard of Dutch Baby until very recently, but now that I have I smile in recognition (it's basically Yorkshire pudding except the fat component isn't beef drippings, it's butter). It's a cute little piece of culinary alchemy--so simple yet never-fail delicious in its transformation. It's a great homage to the power of cast iron.
Here's some photos of someone else's. Oh, here's another; that looks more like my recipe, and the results look more like mine too. And another! And another. I can't help it! It's fun to watch it puff up. :)