Step 1: Make the spice mix: Place the pimento berries, peppercorns, cinnamon, nutmeg, and pimento leaves (or bay leaves) in a spice mill and grind to a fine powder. You may need to work in several batches.
Step 2: Finish the jerk paste: Cut the scotch bonnets in half. For milder jerk chicken, seed them; for more fiery jerk remove the seeds. (Wear rubber gloves.) Cut the scallions crosswise into 1 inch pieces. Rough chop the garlic and ginger. Place the chiles, scallions, garlic, ginger, thyme, and the ground spices in a food processor and finely chop. Add the soy sauce, olive oil, vinegar, rum, lime juice, molasses, and salt and pepper and process to form a thick paste.