Brown pancetta in a large saucepan over high heat until fat is rendered, for about 5 minutes. Remove pancetta from the pan with a slotted spoon and set aside, leaving the grease in the pan.
Melt butter in the saucepan, once hot add onion and garlic and saute until soft, about 4 minutes.
Add brussels sprouts, chicken stock, salt and pepper. Bring chicken stock to a boil, reduce heat down to low and then cover. Cook for about 10 minutes until brussels are fork tender.
Uncover and stir in cream and nutmeg (if using). Turn heat back to high and cook until liquid is reduced and thickened, for approximately 5 minutes. Add cooked pancetta, season with salt and pepper to taste, then stir and serve.