Croque monsieur

1. Put all 4 slices of bread onto a board. Spread the softened butter over each slice, then place it buttered-side down. Melt the remaining butter in a small saucepan over a medium heat. When melted, whisk in the flour and cook for 1-2 minutes until the flour feels sandy and smells biscuity. Take the pan from the heat and gradually whisk in the milk. Return to the heat and bring it to a simmer, whisking until you have a thick and spreadable mixture. Remove from the heat and whisk in the cheese until it starts to melt. Return the pan to the heat briefly if needed to fully melt the cheese, then whisk in the egg yolk, followed by the mustard.

2. Spread the Gruyère mixture over 2 of the slices of bread, then top with the ham. Place the remaining slices of bread on top, so that each sandwich has butter on the outside.

3. Warm a frying pan over a medium heat. Place the sandwiches in the pan and fry for 2-3 minutes or until golden and crisp. Turn over and repeat on the other side. Serve with dressed salad.