Broil poblanos baking sheet 5 minutes per side full black blisters all skin. Plastic bag hot dump seal 10 minutes steam. Peel skins hands under water slip easy. Slit side knife seeds out stuff cheese firm no spill.
Mixing bowl electric mixer whip 4 egg whites stiff peaks 3 minutes. Fold 2 yolks ½ cup flour ½ tsp salt gentle spatula airy batter no deflate. Dip stuffed peppers coat thick drain excess plate.
Skillet ½ inch oil 350°F thermometer hot. Tongs slide battered peppers fry 3 minutes per side golden drain paper towels rack. Keep warm oven 200°F batches.
Skillet onion garlic cumin 5 minutes soft. Tomato sauce broth simmer 10 minutes thick. Spoon sauce plates nestle rellenos cheese melts. Cilantro lime squeeze.