Preheat your oven to 425°F and place your cast iron skillet inside while it heats up. This step is key for that beautiful puff!
In a mixing bowl, whisk together the eggs, sourdough discard, milk, melted butter, sugar, vanilla, and salt until smooth.
Carefully remove the hot skillet from the oven and add butter. Place back in the oven until melted.
Once the butter is melted, take the pan out and swirl the butter to coat the bottom. Pour the batter into the hot skillet and immediately return it to the oven.
Bake for 18–22 minutes, or until the edges are puffed and golden brown.
Remove from the oven (watch it deflate just a little—it’s part of the charm!) and dust generously with powdered sugar.
Top with fresh fruit and serve right away.