In this traditional Cuban specialty, guava paste is sandwiched between layers of Swiss cheese and bread.
Heat oven to 200 degrees. Spread 2 teaspoons butter over cut sides of each roll. Arrange Swiss cheese in a single layer, without overlapping the edges, over bottom halves.
Slice the guava paste into 1/8-inch-thick slices long enough to cover the roll, and place over cheese. Top with another layer of cheese, and close sandwich. Repeat with remaining rolls. Spread the remaining butter over the tops and bottoms of rolls.
Heat a griddle or large cast-iron skillet over medium-high heat. Working in batches, place sandwiches on griddle. Place another heavy pan on top of sandwiches, and cook until golden brown, about 5 minutes. Turn sandwiches over; cook other sides until golden brown and cheese has melted, about 5 minutes more. Remove from heat; transfer to warm oven. Cook remaining sandwiches. Slice in half crosswise, and serve hot.