01 - Boil tomatoes in a pot of water for 5-6 minutes until skins split. Drain thoroughly and transfer to blender. Add garlic, onion, serrano chilies if using, cumin, salt, and pepper. Blend until completely smooth.
02 - Heat 2 tablespoons vegetable oil in a large skillet over medium heat. Pour blended tomato sauce into skillet and simmer for 7-10 minutes, stirring occasionally, until sauce thickens slightly. Taste and adjust seasoning as needed.
03 - Heat small amount of oil in separate skillet over medium heat. Fry tortillas one at a time for approximately 10 seconds per side just until soft and pliable. Drain briefly on paper towels to remove excess oil.
04 - Dip each fried tortilla into hot tomato sauce, coating both sides completely. Place on plate, add cheese filling, and fold in half or roll up. Continue process until all tortillas are assembled.
05 - Arrange 3 entomatadas on each serving plate. Drizzle additional tomato sauce over top, sprinkle with extra cheese, diced onion, and fresh cilantro. Add dollop of sour cream or crema to finish.