What does Boxing Day have to do with boxing?
mid-14c., "meat or fruit pie," crustade, from Middle French croustade (Modern French coutarde), from Old Provençal croustado "fruit tart," literally "something covered with crust," from crosta "crust," from Latin crusta (see crust (n.)). Modern meaning is c.1600. Spelling change perhaps by influence of mustard.
mixture of eggs, milk, sugar, and flavourings which attains its consistency by the coagulation of the egg protein by heat. Baked custard contains whole eggs, which cause the dish to solidify to a gel. Flan, or creme caramel, is a custard baked in a dish coated with caramelized sugar that forms a sauce when the custard is unmolded. For creme brulee, the baked custard is sprinkled with sugar that is caramelized under a broiler or with a hot iron called a salamander. The sugar forms a thin, crisp shell over the custard.