Homemade vegetable stock - Marmite

Ingredients

• 1 leek, washed, thickly sliced
• 1 large carrot, peeled, thickly sliced
• 2 celery stalks, thickly sliced, plus leaves
• 2 onions, peeled, roughly chopped
• 100g mushrooms, brushed, quartered
• 1 medium potato, thickly sliced
• 1 tomato, quartered
• 3 parsley leaves and stalks
• 2 bay leaves
• 4 sprigs thyme
• 4 tbs Marmite