On a baking sheet, broil tomatillos, onion, garlic, and serranos for 8 to 10 minutes. Transfer the roasted vegetables to a blender.
Add cumin, cilantro, chicken stock, flour, and salt, and purée until smooth.
Heat olive oil in a large skillet. Pour in blended sauce carefully to avoid too much splatter and bring it to a boil. Lower heat and simmer till thickened for about 6 to 8 minutes.
Cut corn tortillas into triangles. In a large skillet heat oil and fry corn tortilla pieces until crunchy. Lower heat to low.
Add 2 cups of sauce and mix only long enough to coat all the tortillas. Top with cheese while still over a low flame and cook just long enough for the cheese to melt.
Remove from heat and sprinkle with onions. Serve with eggs any style and top with crumbled queso fresco.
8 medium tomatillos equals about 1 pound.
Tortilla chips: I prefer frying my own tortilla chips. Not only is it a great way to use up a stack of tortillas, but the texture is also heartier, making them better for standing up to the sauce. See baking option below.
To bake chips: Preheat the oven to 400 degrees F. Brush both sides of each tortilla lightly with oil. Cut corn tortillas into quarters. Arrange tortillas on a cookie sheet and bake for 5 to 10 minutes until crispy.
Store-bought salsa verde: I highly recommend you make this easy sauce, but feel free to use your favorite store-bought salsa verde.