Mini Welsh Beef Burgers with Gorgonzola - Gorgonzola DOP

Ingredients

• 500g Welsh Beef, minced
• 2 tsp English mustard
• 1 clove of garlic, crushed
• 1 egg yolk
• salt and cracked black pepper
• 80g Gorgonzola piccante, crumbled
• 2 tbsp mayonnaise
• 8 mini or 4 large burger buns
• salad leaves, to serve
• 1 large red onion, sliced
• small knob of butter
• 1 tbsp brown sugar
• 2 tbsp balsamic vinegar