Cook macaroni according to package directions; rinse, drain and reserve.
Preheat oven to 350°F.
Melt butter in large saucepan until sizzling. Add mushrooms, leeks, and garlic, and sauté over medium heat approximately 5 minutes, or until the mushrooms are tender. Add cream, stir, and bring to a simmer. Reduce heat to low; add cheeses, stirring constantly, just until melted. Stir in the mustard, salt, pepper, artichokes, and 3 tablespoons of chives. Cook, stirring occasionally, for 3 minutes.
Gently stir in cooked macaroni, mixing well. Spoon into a buttered 3-quart, oven-proof baking dish. Sprinkle with breadcrumbs, and bake for 20 to 25 minutes or until top is browned. Sprinkle with remaining 1 tablespoon of chives before serving.