These toasts with a side salad are perfect for serving at dinnertime.

Set the oven rack in the center of the oven. Preheat the oven to 400°F (200°C).
Butter one side of the bread slices and put the buttered side down on a baking sheet.
In a bowl, whisk the egg and mustard until smooth with no trace of egg white.
Add cheese, salt and pepper and mix with a spoon.
Spread the mixture on the slices of bread and bake for 15 to 20 minutes until puffed and golden. Serve immediately.