Bread, ham, gruyere, mustard, butter, egg, cream cheese.
2) Spread cream cheese and grainy mustard onto another slice of bread and put this on top of the ham and gruyere with the plain side facing up.
3) Press the bread with your fingertips so that a shallow well forms in the centre - the idea being that the crust is high enough for the egg not to slide off.
4) Crack an egg and drop into the centre of the bread. If the egg white has pooled in the centre then it will take too long to cook so try to keep the well as shallow as possible and spread the white fairly evenly across the bread.
5) Bake in the oven until the egg white has just begun to form. Serve with a knife and fork!
This dish may take some practise as you want the yolk to remain liquid so that when you cut into the sandwich it flows into the melted cheese and ham. Some people prefer to fry the egg separately and add to the top of the bread - personally I think the sandwich is improved by the egg soaking into the bread a little before it crisps.