2 large onions, thinly sliced 20g butter 1 tsp olive oil 1 tsp light brown sugar
1 tsp balsamic vinegar 4 thick slices sourdough 2 tsp fig jam 120g Gruyere, grated
1 tsp Dijon mustard Softened butter, for the bread Salt and black pepper
Method
Melt the butter with the olive oil in a frying pan over medium-low heat.
Add the onions and a pinch of salt. Cook 18-20 minutes, stirring regularly, until very soft and golden.
Stir in the brown sugar and balsamic vinegar. Cook 2 more minutes until sticky, then season.
Spread the outside of each bread slice with softened butter. Spread Dijon over two inside faces and fig jam thinly over the other two.
Divide the Gruyere and onions between two slices. Close the sandwiches, buttered sides facing out.
Cook in a clean frying pan over medium-low heat for 4-5 minutes per side, pressing lightly.
Rest 1 minute, then cut each toastie in half and serve immediately.
Tap to reveal the secret seasoningFig jam – just one thin layer deepens the caramelised onions and balances the nutty, salty Gruyere without making the toastie sugary.