Place the poblano peppers over an open flame or under the broiler, turning until the skin is charred on all sides. Transfer them to a covered bowl and let them steam for 10 minutes. Peel off the charred skin, then make a small slit in each pepper and remove the seeds.

Stuff each pepper with shredded cheese, carefully closing the slit. In a mixing bowl, beat the egg whites until stiff peaks form, then gently fold in the egg yolks and salt.

Lightly dredge each stuffed pepper in flour, then dip it into the egg batter. Heat oil in a frying pan over medium heat and fry each chile until golden brown on both sides. Transfer to a paper towel-lined plate to drain excess oil.

In a blender, puree the tomatoes, onion, garlic, cumin, salt, and pepper. Heat oil in a saucepan and cook the sauce for 10 minutes. Add broth and simmer for another 5 minutes. Serve the chiles rellenos with the sauce drizzled on top and enjoy!