3 pounds onions, cut into 1/4 inch thick slices
2 pounds (about 6) leeks, the white and pale green parts both, split lengthwise, washed well, and chopped
1/2 pound shallots, cut into 1/4 inch thick slices
1/2 stick (1/4 cup) unsalted butter
1/4 cup heavy cream
1 cup coarse fresh bread crumbs
1 cup grated extrasharp Cheddar (about 1/4 pound)
1/4 teaspoon paprika