Prepare the grill for medium-high heat (375°F). I like to have one burner on high and one on low to place the foil packet over.
In a bowl, toss the carrots with olive oil and season generously with salt and pepper.
Pile the carrots on a double layer of aluminum foil. Nestle the rosemary and garlic in the pile of carrots.
Scatter the butter cubes over the carrots.
Fold up and seal the foil packet.
Place (on the low heat burner or slightly cooler side of the grill) and cook for 10 minutes.
Remove from the heat and carefully open the foil packet and stir the carrots. Seal the foil packet again, return it to the grill, and cook until the carrots are tender, about 10 minutes more.
Discard the rosemary and garlic before serving.
Notes
Double up--Use a double layer of foil when making your foil packet to help prevent drips and flareups if one layer of the foil rips while cooking.
Avoid burns--Be careful when opening your foil packet as there will be hot steam trapped inside.
Dietary--This grilled carrots recipe is suitable for gluten-free and vegetarian diets. To make it vegan, use a little extra oil instead of butter.