Fire up enough charcoal to form a single layer beneath the duck breasts. Rub breasts with salt and pepper under and over the skin. In a blender, combine butter, sage and garlic, blending until the mixture is smooth. Rub equal portions of the seasoned butter under and over the skin.
When the charcoal is covered with gray ash, place the breasts skin-side down over the hot coals. Grill 4 to 5 minutes, until the skin is well browned and crispy. Turn the breasts over, and move them a few inches from the hottest part of the fire, grilling another 2 to 4 minutes for medium rare meat. The butter dripping on the coals may cause some flare-ups, so watch the grill carefully and douse any conflagrations.
Let the breasts sit at room temperature for 5 minutes, and then slice each on the diagonal, serving some of the crispy skin with each breas Tbsp Transfer the slices to a platter or individual plates for serving.
Servings: