Preheat the ovent to 425º F.

Butter and 8 by 10-inch casserole dish.

In a large saucepan or Dutch oven, render the bacon over medium heat. Remove the bacon with a slotted spoon and drain all but 2 tablespoons of the bacon fat. Add the leeks and cook over medium-low heat until tender, about 5 to 7 minutes. Add the swiss chard to the pot in batches, stirring until wilted before adding the next batch. Cook, stirring, until most of the liquid has evaporated, about 8 to 10 minutes. Add the Balsamella, mascarpone, gruyere and parmesan and stir until the cheese has melted.

Pour the leek and swiss chard mixture into the baking dish. Sprinkle the breadcrumbs over the top and bake, until bubbly and golden brown, about 20 minutes.

Serve immediately.