01 -
Preheat the oven to 400°F. Bring a large pot of salted water to a boil. Add Brussels sprouts and cook until just fork-tender, approximately 4 to 5 minutes. Drain thoroughly and set aside.
02 -
In a large oven-safe skillet over medium heat, melt the butter. Add the diced onion and cook until softened, about 3 to 4 minutes.
03 -
Stir in the minced garlic and crushed red pepper flakes, cooking for 30 seconds until fragrant.
04 -
Sprinkle the all-purpose flour over the onion mixture, stirring constantly for 1 minute to create a roux.
05 -
Gradually whisk in the chicken broth. Once the sauce thickens slightly, pour in the heavy whipping cream. Whisk continuously until the sauce is smooth and creamy, about 2 to 3 minutes.
06 -
Season the creamy sauce with kosher salt and black pepper, stirring to combine.
07 -
Add the cooked Brussels sprouts to the skillet and gently fold to coat each piece evenly in the sauce.
08 -
Sprinkle the shredded Gruyère and grated Parmesan evenly over the top. Transfer the skillet to the oven and bake until the cheese is golden and bubbly, about 20 minutes.
09 -
Remove from the oven and garnish with freshly chopped parsley before serving.