Steps
1. Preheat the oven to 200°C (400°F).
2. Prepare the béchamel sauce: melt butter in a saucepan over medium heat. Stir in flour and cook for 1-2 minutes.
3. Gradually whisk in milk, stirring constantly until thickened. Season with salt and pepper.
4. Toast the bread slices lightly.
5. Place one slice of bread on a baking tray, layer with ham and half of the grated Gruyère cheese, then top with the second slice of bread.
6. Spread béchamel sauce over the top slice and sprinkle remaining Gruyère cheese generously.
7. Bake in the oven for 10-12 minutes until the cheese is melted and golden.
8. Meanwhile, fry the egg sunny side up (English style) with a runny yolk.
9. Remove the sandwich from the oven, carefully place the fried egg on top.
10. Garnish with chopped fresh parsley and serve immediately.