Step 1

Real Talk: The key to getting a big, light, puffy rise is to make sure the flour is thoroughly incorporated into the egg mixture. Whisk your arm off until zero, absolutely zero, clumps remain.

Step 2

Place a 10" cast-iron skillet in oven; preheat to 425°. Whisk eggs, milk, and 1 tsp. mustard in a medium bowl until smooth. Whisking constantly, gradually add flour, whisking until smooth; season with salt. Stir in half of cheese and ½ tsp. pepper.

Step 3

Carefully remove preheated skillet from oven and add butter; swirl skillet to coat. Drape half of pastrami into skillet (it’s okay if it bends and folds over itself); season with salt and pepper. Pour egg mixture over. Return skillet to oven and bake until Dutch baby is puffed and golden brown, 12–15 minutes.

Step 4

Remove skillet from oven and heat broiler (do not fear the broiler). Drape remaining pastrami over Dutch baby; top with remaining 2 oz. cheese. Broil until cheese is melted, about 3 minutes.

Step 5

Top with sauerkraut and mustard before serving.