The Creamiest Brussels Sprouts in the Universe

1. Preheat the oven to 375°F. Lightly grease a 3-quart casserole dish with nonstick spray.

2. Make the Caramelized Onions: In a medium skillet, heat the olive oil and butter over medium-low heat. Add the onion; season with salt and pepper. Reduce the heat to low and cook, stirring occasionally, until the onion begins to brown and caramelize, 25 to 30 minutes.

3. Make the Creamed Brussels Sprouts: While the onion caramelizes, melt the butter in a medium saucepan over medium heat. Stir in the flour and cook, stirring constantly, for 1 minute.

4. Add the milk and cream to the saucepan and bring to a simmer over medium heat, stirring constantly. Reduce the heat to low and stir in the Gruyère and nutmeg; season with salt and pepper. Stir until the cheese is melted.

5. Add the brussels sprouts to the saucepan and stir well to coat in the sauce. Transfer the creamed brussels sprouts to the casserole dish and bake until the sauce bubbles and the brussels sprouts are tender, 25 to 30 minutes.

6. Make the Crispy Sage: Heat the oil in a small skillet over medium heat. Add the sage and cook until crisp, 40 to 45 seconds.

7. Top the brussels sprouts with the caramelized onions and crispy sage.