Combine butter, jalapeno, and garlic in a small saucepan over low heat. Cook until the butter melts, stirring occasionally. Season to taste with salt and pepper, and reduce to a warm setting to keep the butter melted.
Preheat grill to medium heat. Place each ear of corn in a sheet of foil.
Brush corn with butter. If you'd like to have the jalapeno on the grill too, scoop some in alongside the corn. Otherwise leave in pan with remaining butter.
Cover grill and cook for 10-15 minutes, turning occasionally. When corn is tender, remove from grill.