This sauce adds depth and richness to your chiles rellenos.

Roughly chop the tomatoes, onion, and garlic.

Add the chopped vegetables, salt, and water into a blender. Blend until completely smooth.

Heat oil in a saucepan over medium heat. Pour in the blended sauce.

Add the tomato purée and dried oregano. Simmer uncovered for 30 minutes, stirring occasionally. Set aside.

This step is key for the smoky flavor that makes authentic Mexican recipes so special.

Roast each poblano directly over a gas burner or under the broiler, turning until blackened on all sides.

Immediately place roasted peppers in a plastic bag or covered bowl for 10 minutes to steam. This makes peeling easier.

Remove from the bag and gently peel off the charred skin using your hands (avoid using water).

Make a vertical slit in each pepper and carefully remove the seeds, keeping the stems intact.

Slice or shred the quesillo (Oaxacan cheese).

Fill each poblano with a moderate amount of cheese, don’t overfill.

Use a toothpick to close the slit and hold the filling inside during frying.

Separate egg whites and yolks into two bowls.

Beat the egg whites with an electric hand mixer until stiff peaks form (about 5 minutes).

Gently fold in the yolks and beat for another 30 seconds.

Heat the oil in a large non-stick frying pan over medium heat.

Place flour on a plate. Roll each pepper in flour until lightly coated.

Dip each floured pepper into the egg batter, covering it completely (except for the stem).

Fry for 1 minute per side or until golden brown. Transfer to a paper towel-lined plate.

Carefully remove the toothpicks from the fried peppers.

Serve the chiles rellenos with warm tomato sauce poured over the top or serve them in the sauce.

Pair with Mexican rice, refried beans, or a side salad for a complete meal.