- Add the oil to a pan, then add the chopped leek and cook over a low to medium heat, stirring frequently, for 4 minutes until it is soft.
- Remove the leek from the heat and allow it to cool for a few minutes.
- Meanwhile, turn on the grill to high and toast one side of the rye bread.
- Add the egg to a bowl with the mustard, and beat lightly. Next, stir in half the grated cheese and all the leek.
- Spread the mixture evenly over the untoasted side of the bread, sprinkle with the remaining cheese and grill for about 2–3 minutes until golden brown.
- Using a mature Cheddar means you can use less and still get a strong flavour.
- Rye bread is an excellent wholegrain – it’s high in fibre and will keep you feeling fuller for longer, so is ideal for breakfast.