Croque-monsieur with smoked ham, cheese and smoked sausage

1.For béchamel, melt butter in a saucepan over medium heat, add flour and whisk continuously until sand-coloured (2-3 minutes), then gradually add milk, whisking continuously. Season to taste, add nutmeg and whisk occasionally until thick and smooth (12-15 minutes). Set aside to cool slightly (5 minutes), then gently whisk in yolk, cover directly with plastic wrap, set aside to cool, then refrigerate until set (20-30 minutes).

2.Meanwhile, for pickled Spanish onion, combine onion, sugar and 1 tsp salt in a bowl, stand until onion is soft (5 minutes), add vinegar and set aside to pickle (20 minutes, or until required).

3.Spread 2 tbsp béchamel onto each slice of bread. Divide ham, pickled Spanish onion, smoked sausage and half the Gruyère among half the bread slices, then sandwich with remaining bread slices with the béchamel side up. Scatter with remaining cheese and refrigerate to set (30 minutes).

4.Preheat oven to 180C. Place sandwiches on a large oven tray lined with baking paper and bake until cheese is melted and bubbling (15-20 minutes). Cut in half and serve warm.