Cut pork shoulder into 2 inch sized pieces. Toss with oil and spices (excluding bay leaves) in a bowl. Add garlic and onion. Squeeze juices from lemons and limes, mix well. Place mixed ingredients into a casserole dish. Add bacon fat/lard, heavy cream and bay leaves to dish. Wrap tightly with two layers of foil, sealing all edges. Place casserole dish on sheet pan. Roast in 275 degree oven for 3.5 hours. Check that meat is fork tender. If not, cook another 15-30 min. Do not overcook. Drain ingredients through a strainer into a bowl. Remove the onions, bay leaves, lemons, limes, and garlic and discard. Replace meat into casserole dish and spoon drained juices over meat. Broil, uncovered for 3 to 5 minutes until tops are crispy. Watch carefully so it doesn't burn. Serve over greens, cauliflower rice, in cheese taco shells, or cabbage "taco shells".