In a large stockpot, add the water and bacon and bring to a boil over high heat. Add the collard greens by handfuls, stirring until each batch is wilted before adding more. Bring to a boil and add the onions. Cover and simmer over moderate heat until the collards are very tender, about 40 minutes. Remove from the heat and let cool, then squeeze the water out of the collards until almost dry. Place collards on a cutting board and coarsely chop.
Meanwhile, in a food processor, combine the dry bread crumbs with the Parmesan, minced parsley, sage, garlic and extra-virgin olive oil. Pulse until just blended.
Preheat the oven to 350 degrees F.
Generously butter a shallow 4-quart casserole. In a large bowl, mix the collards with the cream and season with salt and pepper. Stir in the eggs until blended and spread the collards into the prepared casserole. Cover with foil and bake for 30 minutes. Remove from the oven and sprinkle the Parmesan crumbs over the collards. Return to the oven and bake for about 20 minutes longer, or until the crumb topping is golden. Preheat the broiler and broil the collards 10 inches from the heat until the bread crumb topping is golden brown and crisp. Serve hot. Tastes great with fried chicken.