Adjust rack to middle position and preheat oven to 425 degrees. Allow ingredients to come to room temperature. Wash and dry produce.

In a large bowl, whisk together half the sour cream, two eggs*, ⅓ cup flour, ¼ cup milk, and a big pinch of salt until smooth (for 4 servings, use all the sour cream, three eggs, ½ cup flour, and ½ cup milk; save remaining egg for another use). (Be sure to measure the milk—we sent more.)

Place 1 TBSP butter (2 TBSP for 4 servings) in a medium ovenproof pan. Once oven is preheated, place pan on middle rack; heat until butter melts and starts to bubble. TIP: Watch carefully to avoid burning.

Once butter has melted, remove pan from oven and carefully swirl once to evenly coat bottom; pour in batter. Bake on middle rack until puffed and golden, 20-25 minutes.

While Dutch baby bakes, dice half the mozzarella (all the mozzarella for 4 servings) into ½-inch pieces. Roughly tear half the prosciutto (all the prosciutto for 4) into thirds (it’s OK if the pieces aren’t perfect—it looks better that way!). TIP: Save any remaining mozzarella and prosciutto for another use.

When Dutch baby has about 2 minutes left, in a medium bowl, toss arugula and half the diced mozzarella with a large drizzle of olive oil.

Top Dutch baby with as much arugula salad, torn prosciutto, and remaining diced mozzarella as you like. Season with pepper and drizzle with balsamic glaze.

Serve family style directly from pan (or cut into wedges and divide between plates).