Preheat the oven to 400˚F.
In a large saucepan, cook the Brussels sprouts in salted boiling water for 5 minutes or until just tender; drain well.
Meanwhile, cook the bacon in a 10-inch cast iron skillet for about 3 to 4 minutes or until desired crispness. Add the parboiled Brussels sprouts to the skillet and continue to cook for 1 minute.
In a mixing bowl, combine the Half & Half (or heavy whipping cream), Dijon mustard, half of the grated parmesan cheese, garlic, salt, pepper, and nutmeg; whisk until well incorporated.
Remove the skillet from the heat and pour the cream sauce over the Brussel sprouts. Sprinkle the remaining parmesan cheese over the sprouts and bake for 15 to 20 minutes, or until bubbly and the top is golden brown.
Remove from oven and let stand several minutes.
Garnish with crushed red pepper flakes and serve.
