Cook onion wedges in 1 C water mixed with 1/2 t salt until tender, covered. Reserve 1 C onion water for sauce. Drain.
Melt 4 T butter. Stir in 2 T flour and cook over medium heat, stirring, for five minutes. Slowly add reserved onion water and whisk until smooth. Add pepper sauce.
Whisk together: light cream and egg. Add a little of the onion sauce and whisk to warm the cream mixture. Add remaining onion sauce and continue whisking over low heat, until it's the consistency of heavy cream. Be careful not to overcook the egg.
Toss sauce with onions and put in a shallow casserole, greased with softened butter.
Top with cubed bread, cheddar and romano cheeses, tossed with 8 T melted butter.
Bake at 350 for 30 - 35 minutes, until top is golden.