Cheesy Leek Casserole

• 1/2 Stick butter
• 1/2 Teaspoon marjoram
• 1^1/2 Garlic cloves, minced
• 1/4 Cup all-purpose flour or GF measure for measure
• 2 Cups milk
• 1 Cup shredded Gruyere or Jarlsberg cheese
• 1/2 Cup shredded Parmesan Reggiano cheese
• Pepper to taste
• 6 Leeks, white and light green portions, rinsed well and thinly sliced
• 4 Slices bacon cooked and crumbled
• 1^1/2 Tablespoons olive oil (extra-virgin)

Preheat an oven to 375°F. Butter a large gratin dish or 8-inch square baking dish.

Rinse the leeks really well and thinly slice.

Melt the butter in a saucepan over medium heat. Add the marjoram and cook, stirring occasionally, until fragrant, about 1 minute. Whisk in the flour and cook, whisking constantly, until golden, about 2 minutes. Slowly whisk in the milk, making sure each addition is fully incorporated before adding more. Add the cheese and cook, stirring frequently, until melted, about 2 minutes. Season to taste with pepper.

Heat the oil in the pot. Add the leeks. Cover and cook over medium to medium low heat, stirring, until tender, 7 minutes. Uncover and add the bacon and garlic, and cook, stirring, until fragrant. (about 2 minutes). Add the leeks to the saucepan, stirring to coat them with the cheese sauce. 

Transfer the mixture to the prepared baking dish. Bake until the top is browned and the leeks are tender in the upper third of the oven for 25 minutes. Let rest for 10 minutes before serving to prevent burning your mouth.