3 onions (about 600g/1lb 5oz), thinly sliced
1 tbsp finely chopped fresh thyme leaves
1 tsp Dijon mustard
salt and freshly ground black pepper
1 level tbsp plain (or gluten-free) flour
1 tbsp brown miso paste
3 tbsp olive oil
600ml/20fl oz hot vegetable stock (homemade or from a stock cube)