Let cheddar, Monterey Jack, and provolone sit at room temp for 15 minutes for smooth melting.
Bake bacon at 400°F (200°C) for 15–20 minutes until crisp. Drain on paper towels.
Warm a skillet or griddle over medium-low heat to avoid burning bread.
Spread butter on one side of each slice, covering edges for even browning.
Place 4 slices buttered side down in skillet. Add cheese, 2 bacon strips, ranch, then top with remaining slices, buttered side up.
Cook 3–4 minutes per side until golden and cheese melts, pressing lightly with spatula.
Rest 1 minute, slice diagonally, and serve hot.