Pour 1 cup (250ml) hot water into a large, deep nonreactive pan, bucket or cooler. Add the molasses and salt and stir until the salt is fully dissolved. Add the peppercorns, lemons, onions, garlic and rosemary. Place the turkey drumsticks in the brine and cover with 8 cups cold water (2 liters). Refrigerate for at least 6 hours (or overnight).
Remove the turkey from the brine and dry thoroughly. Season with salt and pepper.
Prepare a charcoal or gas grill for indirect cooking. If you are using a charcoal grill, place 10 to 12 charcoal briquettes on only one side of the grill. Heat to 400 degrees F (200 degrees C).
Place the turkey drumsticks on the grill on the opposite side of the charcoal. Brush with melted butter and close the lid. Cook, turning the drumsticks and basting with butter every 30 minutes, until a meat thermometer inserted into the thickest part of the thighs registers 160 degrees F (75 degrees C), about 2 hours.
Before serving, brush the drumsticks with pureed chipotles.