Mushroom wellington burger

Ingredients

• 200 g Australian button mushrooms
• 1 tbsp vegetable oil
• 1 small onion
• 1 clove garlic
• 4 sprigs thyme, leaves stripped
• salt and pepper, to season
• 300 g beef mince (around 20% fat)
• 1 egg
• 8 thin strips prosciutto
• 4 Martin’s potato rolls or similar (potato or brioche-style roll)
• Dijon mustard, to serve
• red onion, thinly sliced on a mandoline
• red oak lettuce, to serve
• 2 cloves garlic
• 25 g butter
• 1 bunch spinach, roughly chopped
• 1 bunch kale, leaves stripped and roughly chopped
• 1 brown onion, peeled and roughly chopped
• ¼ cup red wine vinegar
• 2 tbsp brown sugar
• 1 cup red wine
• 2 cups tomato sauce (ketchup)