Fill a medium-sized pot with water, add the teaspoon of salt and bring to a boil. Add the slices of güisquil and simmer for 10 minutes or until slightly tender. Drain and set aside.
In a skillet over medium heat, add 1 tbsp of oil and sauté the chopped tomatoes, onion and minced garlic with the seasonings for about 5 minutes. Once cooked, blend the mixture into a smooth sauce using some of the güisquil cooking water as needed to thin out the sauce to a slightly thinner consistency.
In the same skillet, add 1 tbsp of oil and fry the blended sauce briefly, about 4–5 minutes, then set aside.
In a medium-sized bowl, beat the egg whites until stiff peaks form, then gently add the egg yolks one by one and beat until it becomes a thick batter.
Place a slice of queso fresco between two slices of güisquil, then dip this into the egg mixture to thoroughly coat all sides.
In a frying pan add the remaining oil over medium-high heat and fry the egg-coated, cheese-stuffed güisquiles until golden brown on both sides, about 5 minutes on each side. Repeat this step until all the güisquiles have been fried.
Place the skillet with the sauce back on the stove over medium heat and add the fried güisquiles. Coat the güisquiles in the sauce and allow them to gently simmer for about 5 minutes.
Serve the Güisquiles Rellenos with a side of rice and enjoy.