Irish Stout Salisbury Steak Burgers

Ingredients

1 kg beef mince
3 tbsp breadcrumbs
1 onion, finely diced
100ml stout
2 tbsp parsley
1 tsp salt
1 tsp black pepper
For the sauce:
1 cup sliced mushrooms
2 cloves garlic, crushed
300ml double cream
200ml beef stock
200ml stout
1/2 tsp salt
1 tsp black pepper
2 tbsp butter
2 tbsp worcestershire sauce
2 tbsp balsamic vinegar