In a skillet over medium-high heat, cook the diced bacon until crisp. Transfer to a plate and set aside.
In a large pot of boiling salted water, cook the pasta until al dente, about 7 minutes.
Meanwhile, in a large saucepan, melt the butter over medium heat. Whisk in the flour to form a roux. Cook for 2-3 minutes, stirring frequently. Gradually add the milk, whisking until smooth and combined. Bring to a simmer.
Whisk in 2 cups shredded cheese, salt, and nutmeg. Continue stirring until melted and smooth.
Remove the sauce from the heat. Drain the pasta. Add the pasta to the sauce and stir to coat. Fold in the bacon, reserving 1 tablespoon for the topping.
Place 4 oven-safe lion head soup bowls or ramekins on a baking sheet. Spoon the macaroni and cheese into the bowls.
Top each bowl with a handful of shredded cheese and reserved bacon. Broil in the oven until the topping is golden brown, about 3 minutes.
Notes
Storage: Store in an airtight container in the refrigerator for up to 5 days.Casserole: To make this in a casserole dish instead of individual ramekins, spoon the macaroni and cheese into an oven-safe baking dish. Top with remaining shredded cheese and bacon. Broil for 2-3 minutes, until the topping is bubbly and golden brown.