Mushroom and red onion toastie

Method

1. Add a splash of oil to a non-stick frying pan, then fry the onion with a pinch of salt for 5 minutes. Add the mushrooms, thyme and the knob of butter, then continue to fry, stirring every so often, until the mushrooms are golden brown. Season again with a little salt and add 2 tsp of the balsamic. Turn the heat down slightly and continue to fry for 2 minutes or so until the onions are nice and sticky. Stir in the remaining 1 tsp balsamic, then set aside in the pan to keep warm.
2. Heat the grill to medium-high. Toast the sourdough, then butter it and layer on the grated cheese. Put under the grill for 2-3 minutes until melted, then top with the sliced blue cheese and stick back under the grill for 1-2 minutes more until bubbling.
3. Top with the mushrooms and onions, then serve scattered with a few more thyme sprigs.