Step 1

Preheat the oven to 425°F

Step 2

Grease a 9x13 baking dish with cooking spray or butter, set aside.In a large skillet, heat 2 tablespoons olive oil over medium heat

Step 3

Add the leeks to the pan and cook for 4 minutes

Step 4

Add the garlic and cook for 1 minute longer.Transfer the leek mixture into a large bowl along with the shredded brussels, toss to combine.Using the same skillet, add the cream, Gruyere, 1/4 cup parmesan, salt, pepper, thyme and nutmeg

Step 5

Bring to a simmer stirring continuously until cheese melts and a thick sauce is achieved, about 3 minutes.Pour the sauce over sprouts and leeks and toss to coat.Transfer the sprouts mixture into the prepared 9x13 baking dish

Step 6

Place it in the oven on the center rack for 20 minutes.In a small bowl, combine the panko with remaining 1/4 cup parmesan and remaining 3 tablespoons of oil.Scatter bread crumb mixture over sprouts and return to oven until golden brown, 5 to 8 minutes.