Broil the pepper on a lined baking sheet, turning as needed, for about 8–10 minutes until blistered. Watch closely. Put it in a covered bowl for 5 minutes, then peel, remove stem and seeds, and dice. Measure ¼ cup and blot away excess moisture; save any remainder for another meal.

Turn off the broiler and set the oven to conventional bake at 350°F (175°C). Grease a 2-quart baking dish. Let the oven settle to the baking temperature before putting in the casserole.

Whisk the sour cream, melted butter, and eggs in a large bowl. Fold in the drained whole-kernel corn, undrained cream-style corn, and measured poblano.

Stir in the corn muffin mix just until no dry pockets remain, then fold in the cheddar. Transfer to the dish and smooth the surface.

Bake for 45–55 minutes, until the top is golden, the edges are set, and the center has no liquid wobble. A skewer should show moist crumbs rather than raw batter. Cover loosely with foil if the surface browns early.

Rest for 10 minutes before serving. Divide into 10 side-dish portions. The middle is meant to be soft and scoopable, not as dry as a loaf of cornbread.