Roast the peppers: Char the poblano peppers directly over an open flame or under your oven broiler until the skins are blackened and blistered. Turn often for even roasting.
Steam and peel: Transfer roasted peppers to a plastic bag and seal for 10 minutes. This steaming step makes peeling easier.
Clean and stuff: Once cooled, gently peel the charred skin, make a small slit down the side of each pepper, remove the seeds, and stuff generously with queso fresco.
Prepare the batter: Separate the eggs. Beat the egg whites with a pinch of salt until stiff peaks form. Then fold in the yolks and 2 tablespoons of flour until smooth.
Coat the peppers: Lightly dust the stuffed peppers with flour. Then dip each into the egg batter, making sure they’re well-coated.
Fry until golden: Heat vegetable oil in a large skillet over medium-high heat. Carefully add each coated pepper and fry until golden brown on all sides, about 3–4 minutes per side. Drain on paper towels.
Make the salsa: Blend all salsa ingredients until smooth. Pour the salsa into a skillet and bring to a light simmer.
Simmer the rellenos: Add the fried peppers into the salsa, cover, and let simmer on low heat for 4–10 minutes. Serve warm and enjoy!