Preheat oven to 425 degrees F.
Melt butter in a small heavy saucepan. Stir in the flour, increase the heat to medium-high and cook for 2 minutes, being careful not to let it brown. Whisk in the milk and heavy cream and cook, stirring constantly, until the mixture comes to a gentle boil. Cook until the floury taste is gone and sauce is smooth and thickened, about 3 minutes. Add the Gruyere and stir until melted. Season with salt, white pepper, and nutmeg. Remove from heat.
In a small bowl, combine bread crumbs, chopped herbs, Parmesan, and olive oil.
Season shrimp with Essence. Layer shrimp and sliced onion in a gratin dish. Cover with Mornay sauce. Top with bread crumb mixture. Bake until golden brown and bubbly, about 20 minutes. Remove from oven and let rest for 10 minutes. Serve over grilled portobellos and eggplant slices.
Yield: 4 servings