Cook the Pork:

Combine the pork shoulder, pork belly, fatback, garlic, bay leaves, thyme, nutmeg, salt, and pepper in a large, heavy-bottomed pot. Add just enough water or stock to cover the meat.
Bring the mixture to a simmer over low heat, then cover and continue to cook gently for about 4-6 hours, stirring occasionally. The meat should be very tender and easily shredded.

Shred the Meat:

Remove the bay leaves and let the mixture cool slightly. Using two forks, shred the meat while removing any large pieces of fat or gristle. The texture should be fine and spreadable.

Reduce the Cooking Liquid:

If there's a lot of liquid remaining, return the pot to the heat and simmer uncovered until the liquid has reduced and the meat mixture is moist but not watery.

Transfer to Containers:

Pack the rillettes into small jars or ramekins, pressing down to eliminate air pockets. Pour a thin layer of melted fat over the top to seal the rillettes. Cover and refrigerate for at least 24 hours to allow the flavors to meld.

Serve:

Serve the rillettes spread on toasted or crusty bread, accompanied by cornichons or pickled onions.