Heat large skillet or griddle to medium-high heat.
Spread 1/2 Tablespoon butter on one side of each tortilla.
Place one tortilla, buttered side down, in the hot skillet. Top with 1/2 cup cheese and 1 cup spinach. Place another tortilla, buttered side up, on the cheese mixture.
Let cook 2-3 minutes, or until tortilla is browned and crispy, then flip and cook on other side 2-3 minutes.
Repeat with remaining tortillas, cheese, and spinach.