Mary Berry's Cottage Pie / Tried and Tested - All Kitchen Colours

Ingredients

• 1 tbsp oil
• 900 g beef mince
• 2 onions (chopped)
• 4 sticks celery (diced)
• 50 g plain flour
• 250 ml red wine
• 300 ml beef stock
• 2 tbsp Worcestershire sauce
• 2 tbsp light muscovado sugar
• 1 tbsp thyme (dry or fresh)
• 250 g small brown chestnut mushrooms (sliced)
• dash of gravy browning (optional)
• salt and pepper
• 1.5 kg King Edward potatoes (peeled and cut into 4mm slices)
• 150 ml double cream
• 100 g strong cheddar (grated)