Cook spinach according to package directions. Allow this to cool and then drain and squeeze out all liquid.

Preheat oven to 375˚F and butter a gratin baking dish.

In a medium saucepan over medium heat, heat olive oil and sauté the onion for 3-4 minutes.

Sprinkle in the flour and continue sautéing while mixing for 30 seconds.

Add the cooked spinach, salt, pepper, dried thyme, and garlic to the pan and stir until the ingredients are combined.

Stir in the milk, heavy cream, and half the Parmesan and Havarti cheese into the spinach mixture. Add nutmeg, mix lightly, and heat through to evaporate liquid. Pour out pan ingredients into the baking dish.

In a medium bowl, stir together melted butter, bread crumbs, and remaining cheese. Mix well. Spoon the mixture evenly over the gratin top. Drizzle olive oil on top.

Bake 15 minutes, until it is hot and bubbly, and the breadcrumbs have turned golden brown.