01 - Boil tomatoes in a pot of water for 5-6 minutes until skins split. Drain and transfer to blender with garlic, onion, serrano chilies, cumin, salt, and pepper. Blend until smooth. Heat 2 tablespoons oil in skillet, pour in tomato sauce and simmer over medium heat for 7-10 minutes, stirring occasionally until slightly thickened. Adjust seasoning as needed.
02 - Heat small amount of oil in separate skillet over medium heat. Lightly fry tortillas one at a time for about 10 seconds per side just until soft and pliable. Drain briefly on paper towel.
03 - Dip each tortilla in hot tomato sauce coating both sides. Lay on plate, fill with cheese, and fold in half or roll up. Repeat with remaining tortillas.
04 - Place 3 entomatadas on each plate. Drizzle with additional tomato sauce, sprinkle with extra cheese, diced onion, and cilantro. Add dollop of sour cream on top.