Prepare a grill for medium heat. If using a charcoal grill, build an even layer of hot coals on the bottom.
For the rice pilaf: Melt the butter and olive oil in a large ovenproof pot or Dutch oven. Add the garlic and onions with a pinch of salt and cook, stirring occasionally, until the onions are softened, 3 to 5 minutes. Add the coriander, cumin and nutmeg and continue to cook to toast the spices, 2 to 3 minutes. Add the rice, stirring to coat, and toast, about 2 minutes. Add the bay leaf and chicken stock. Bring to a gentle boil then season with salt and cover the pot. Cover the grill and cook until the rice is cooked and all the liquid is gone, about 18 minutes.
Meanwhile, prepare the foil packets for the clams with sausage and peppers: Lay out a double layer of large heavy-duty aluminum foil pieces in an X formation, totaling 2 packets. Distribute the garlic, peppers and onions evenly between the packets. Top each with the clams and sausage. Bring up all 4 sides of the foil, but don't seal. Divide the stock, wine and butter between each packet. Season with salt and pepper. Tightly seal the foil.
Remove the rice from the grill, remove the lid and fluff with a fork. Place a kitchen towel over the pot and place the lid of the pot back over the kitchen towel. Let sit for 10 minutes without opening. This will help absorb the moisture in the pot so the rice is fluffy and not mushy.
Remove the ring from the grill if it has one so the coals are exposed and place the packets directly onto the coals. Steam until the clams open and everything is heated through, 7 to 8 minutes.
When ready to serve, transfer the rice pilaf to a serving plate. Carefully open the foil packets and pour everything over the rice pilaf, making sure to get all the juices from the packets. Sprinkle with cilantro leaves, drizzle with some olive oil and serve!
(Alternatively, you can cook the rice pilaf in a 350 degrees F oven for 18 minutes and bake the clams with sausage and peppers foil packets in a 375 degrees F oven for 8 to 10 minutes.)