In a large heavy skillet cook onions, leeks and shallots in butter with salt and pepper to taste. Covered over medium heat, stirring occasionally for approx. 10 min

Reduce heat to moderate-low, continue to stir occasionally 10-20 min until soft. Remove lid and cook over moderate heat for another 3-5 minutes until excess liquid is evaporated

Transfer Onion mixture to a 2 quart shallow baking dish. Stir in heavy cream. Top with cheese then breadcrumbs. Dust with paperika

Heat oven to 375o and cook for 20-30 minutes