Ultimate toad-in-the-hole with caramelised onion gravy

Name: Ultimate toad-in-the-hole with caramelised onion gravy
Prep time: 20 min
Cook time: 40 min
Total time: 1 h
Cuisine: British
Ingredients: 140g plain flour; 4 large eggs; 300ml semi-skimmed milk; 1 tbsp wholegrain mustard; handful of woody herbs, leaves picked and chopped (we used 6 sage leaves, 4 rosemary sprigs and 4 thyme sprigs), plus a handful, fried until crispy, to serve (optional); 2 tbsp sunflower oil; 8 rashers smoked streaky bacon; 8 fat sausages (we used Cumberland but use your favourite variety); 2 red onions, cut into wedges; cooked green vegetables (optional), to serve; mash (optional), to serve; drizzle of sunflower oil; 2 red onions , halved and thinly sliced; 1 tbsp golden caster sugar; 2 tbsp balsamic vinegar; 2 tbsp plain flour; 250ml red wine; 500ml chicken or beef stock