With the rack in the middle position, preheat the oven to 200 °C (400 °F). Butter a 23 x 13-cm (9 x 5-inch) loaf pan.
In a skillet over medium heat, soften leek in butter. Let cool.
In a large bowl, beat eggs with milk. Add bread and let soak for about 5 minutes. Add meat, cheese and cooled leek mixture. Mix thoroughly with your hands until mixture is smooth. Season with salt and pepper. Pour into the loaf pan.
Bake for 1 hour and 15 minutes. Let rest for 15 minutes before slicing.
Meanwhile, in the same skillet over medium-high heat, brown mushrooms in butter. Sprinkle with flour and mix thoroughly. Add milk, broth and garlic and bring to a boil, whisking constantly. Simmer until sauce thickens. Adjust seasoning. Sprinkle with fresh thyme leaves, if desired.
Serve the meatloaf with the sauce, mashed potatoes and green beans, if desired.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.