Heat skillet set over medium heat. Cook bacon 5 to 8 min. or until it begins to crisp. Transfer to paper towel to drain. Drain fat from skillet. Add butter and leeks. Cook 5 to 8 min. until tender. Cool completely.
Preheat oven to 325°F (160°C). In bowl, whisk eggs with cream, salt and pepper. Whisk in 1/2 cup (125 mL) cheese, chives and the reserved bacon and leeks. Dip panettone slices in egg mixture. Transfer to greased 9 x 13-in. (3 L) baking dish. Pour remaining mixture over bread, and refrigerate for at least 30 min. or until bread absorbs the egg mixture. (Or make ahead to this step and cover and refrigerate overnight).
Sprinkle with remaining cheese. Cover with foil and bake 30 min. Uncover, continue to bake another 20 to 30 min. or until golden brown and set in centre. Serve with maple syrup.