How to Make It
In a large saucepan, combine the tomatillos and jalapeño and add 8 cups of water. Bring to a boil, then simmer over moderate heat, stirring, until the tomatillos are very soft but not falling apart, about 15 minutes. Using a slotted spoon, transfer the tomatillos to a blender. Add 1 cup of the cooking liquid to the blender. Add the chopped cilantro and garlic cloves and puree until smooth. Season the salsa with salt and pepper. Discard the remaining cooking liquid.
In a large skillet, heat 2 tablespoons of the oil. Add the onion and cook over moderate heat, stirring occasionally, until golden, 7 to 8 minutes. Stir in the tomatillo salsa and simmer for 5 minutes. Dip 1 tostada at a time in the tomatillo salsa, turning, until some of the salsa is absorbed but the tostada still holds its shape, about 15 seconds. Transfer the tostada to a large plate; repeat with the remaining tostadas. Transfer the remaining salsa to a bowl.
In a large nonstick skillet, heat the remaining 2 tablespoons of oil. Crack the eggs into the skillet and cook sunny-side up over moderate heat, 3 to 4 minutes.
Place 1 tostada on each of 4 plates. Spoon some of the beans on top and cover with another tostada. Repeat with the remaining beans and 4 remaining tostadas. Top each stack with a fried egg. Garnish with the radishes, jalapeños, queso fresco and cilantro sprigs and serve with the remaining salsa.