SLICE serrano chiles lengthwise in half. Remove seeds and veins. Thinly slice into lengthwise strips. (Wear gloves to protect hands.)
HEAT olive oil in a small frying pan. Add chile strips and cook over medium heat 3 to 4 minutes, stirring constantly until chiles begin to blister and soften.
ADD soy sauce and raisins. Cook 30 seconds or until liquid is nearly evaporated. Remove from heat and set aside. (Be sure to work in a well-vented area.)
HEAT a wide frying pan over medium heat. Brown one side of one tortilla; flip tortilla over and place one fourth of the cheese and cooked chiles on half the tortilla. Fold the other half of the tortilla over the filling. Continue to cook over medium heat, turning once to brown the other side. Repeat with remaining tortillas.
CUT quesadillas in wedges and serve with sour cream and cilantro.