Butter the bread and spread with marmalade and make into three sandwiches. Spread the top of each sandwich with some more butter, and cut each into four triangles. Stand the triangles, butter side up, in an oven proof dish. Beat the egg together with the cream, milk and caster sugar and pour over the bread. Mix the demerera sugar, citrus peel and crystallized peel together and sprinkle over the top. Bake in a medium oven until 'custard' is firm and tips of sandwiches are golden and crispy. Serve with cream or créme fraiche,