10 to 12 large ears of corn, shucked
4 tablespoons (1/2 stick) butter, divided
2 cups chopped onions
1 cup chopped celery
2 1/2 teaspoons coarse kosher salt, divided
4 large eggs, separated
1/2 cup crème fraîche or sour cream
1/8 teaspoon freshly ground black pepper
PreparationUsing large holes on box grater, grate enough corn into large measuring cup to yield 4 generous cups of thick milky pulp.
Preheat oven to 425°F. Melt 2 tablespoons butter in heavy large skillet over medium-low heat. Add onions and celery; sprinkle with 1/2 teaspoon coarse salt. Sauté until tender but not brown, 10 to 12 minutes. Scrape mixture into bowl.
Whisk egg yolks in large bowl 2 minutes. Stir in corn mixture, onion mixture, crême fraîche, 1/8 teaspoon pepper, and remaining 2 teaspoons coarse salt. Whisk egg whites in medium bowl until stiff but not dry; fold into corn batter in 2 additions.
Place remaining 2 tablespoons butter in 10- to 12-cup cast-iron skillet or baking dish. Transfer to oven and heat until butter begins to brown, about 4 minutes. Brush butter over inside of skillet. Add pudding.
Bake pudding 15 minutes. Reduce oven temperature to 350°F. Bake pudding until set and golden, about 30 minutes longer. Let stand 5 to 10 minutes before serving.