Start by steaming the broccoli florets in a microwave or on the stovetop until they are crisp-tender, about 5 minutes. Drain and set aside.

Preheat your oven to 425°F (220°C) and grease an 11x7-inch baking dish with olive oil.

In a large skillet, heat 2 tablespoons of olive oil over medium-high heat. Add leeks and shallots and cook for 8-10 minutes. Stir in minced garlic for the last 1-2 minutes.

Add dry white wine to the skillet and let it cook until mostly evaporated, about 3-4 minutes. Sprinkle in the flour, whisking continuously, then gradually add milk, stirring until thickened, about 4-5 minutes. Season with salt and pepper.

Fold in the steamed broccoli into the sauce, ensuring it's evenly coated.

In a separate bowl, combine remaining olive oil with panko breadcrumbs, mixing until coated.

Transfer the broccoli mixture into the baking dish and top with the panko breadcrumb mixture. Bake uncovered for about 20 minutes until bubbly and golden-brown.