Toad-in-the-hole with red onions & thyme batter

INGREDIENTS

• 1 red onion , cut into wedges, layers separated
• 8 thick low-fat pork sausages
• 1 tsp olive oil
• 100g plain flour
• 1 medium egg
• 300ml skimmed milk
• 2 tsp wholegrain mustard
• 1 tsp fresh thyme leaves
• steamed carrots and cabbage, to serve