Heat the butter in a large skillet over medium heat. Add the onions and cook, stirring, for about one minute. Alternate adding the flour and milk, stirring constantly to make a smooth and thick white sauce. Remove from the heat. Add the crabmeat, saltine cracker crumbs, egg, salt, cayenne and hot sauce. Gently mix together and set aside to cool completely. (If you wish, you can chill the mixture in the refrigerator.)

Gently shape into six patties. Dredge them in the cracker meal or bread crumbs, coating completely and evenly.

Put about one-half inch of equal parts of butter and vegetable oil in a nonstick skillet over medium heat. Fry the patties two to three minutes on each side until golden brown. Drain on paper towels and serve warm.