Directions

1. In a medium saucepan, melt 1 tablespoon butter over medium-high. Cook onion, stirring often, until lightly browned, 5 minutes. Add 3 cups water, rosemary, 2 teaspoons salt, and 1/4 teaspoon pepper; bring to a boil.
2. Whisking constantly, gradually add cornmeal, whisking until incorporated before adding more. Reduce to a simmer; cook, whisking frequently, until thickened, about 5 minutes. Remove from heat; stir in corn, remaining 3 tablespoons butter, and half the cheese until melted.
3. Place peppers in a large baking dish; fill with polenta mixture. Cool to room temperature. Cover tightly with foil; refrigerate until ready to use, up to 2 days.
4. Preheat oven to 400 degrees. Pour 1/2 cup water in bottom of baking dish. Cover with foil; bake 30 minutes. Remove foil; sprinkle with remaining cheese.
5. Return to oven; bake, uncovered, until cheese is golden and peppers are very tender, about 30 minutes more. Serve immediately.