Cut bread crosswise into 12 slices about 1/2 inch thick. Lightly spread both sides of each slice with butter. Cut cheese across the widest dimension into 1/4-inch-thick slices.
Layer 3 bread slices with enough cheese between slices to cover bread. Cut stack into quarters. Push cut end of a rosemary sprig through each quarter-stack of bread and cheese to hold layers together. Repeat to use remaining bread, cheese, and rosemary. If needed for stability, push toothpicks into stacks parallel to rosemary sprigs. Season to taste with salt and pepper.
Lightly oil a barbecue grill over a solid bed of hot coals or a gas grill on high heat (you can hold your hand at grill level only 2 to 3 seconds). Lay skewered bread and cheese on grill. Close lid on gas grill. Cook, turning often, until bread is lightly toasted, 2 to 5 minutes. Serve spiedini hot.