The key to the dish’s dramatic puff comes from oven spring—the jolt of heat and steam the batter gets when it’s poured into a sizzling hot pan and placed in a cranked-up oven. The butter browns instantly when it’s added to the pan, but pouring in the batter right away keeps it from burning, and the brown butter lends rich nuttiness to the batter. Make the strawberry topping first so the fruit has time to macerate and release some of its juice to form a loose sauce. The finished Dutch baby will deflate a little as it cools, though the texture remains airy and crisp outside, creamy and custardy within.
Hull and quarter strawberries; place in a medium bowl. Add sugar, 1 teaspoon lemon rind, and juice; toss.
Place a 10-inch cast-iron skillet in oven; preheat to 450°F.
Combine cornstarch, milk, flour, eggs, egg white, remaining 1 teaspoon lemon rind, and 1 tablespoon butter in a blender; blend until smooth.
Once oven is preheated, remove pan. Coat pan with cooking spray. Add remaining 1 1/2 tablespoons butter to pan; swirl to coat. Add batter to pan; bake at 450°F for 20 minutes or until batter is very puffed and deeply browned. Remove from oven. Top with strawberry mixture; sprinkle with nuts. Slice into quarters; serve immediately.