Cut the pumpkin in half carefully using a knife or heavy cleaver. Hollow out the seeds and stringy bits with a spoon. Slice off the rind, and cut into chunks.

To a large dutch oven over medium heat, add the butter, leeks (or onion), and thyme. Cook for 5 minutes, until softened but not browned.

Add the pumpkin chunks, stock, and bay leaf. Bring to a boil, then turn the heat down to a simmer. Cover the pot, and cook for 35 minutes, or until the pumpkin is very tender. Remove the bay leaf and thyme sprigs.

Off the heat, use an immersion blender to get the soup to a smooth, creamy texture (or pour into a blender or food processor in batches.) Stir in the cheese. Once melted, blend (or whisk) once again so the cheese is totally emulsified into the soup.

Stir in the salt, pepper, nutmeg, and cream (if using). At this point you can keep the soup warm over low heat, but don’t let it come back up to a boil, or the cream will split (which will make the soup grainy).

Serve the soup in bowls, garnished with chopped chives or whatever garnishes you like (crumbled bacon, homemade croutons, fried sage, toasted nuts or pumpkin seeds are all great options).