Vegan Cottage Pie (Shepherd's Pie) - The Pesky Vegan

Ingredients

• 1 tablespoon olive oil
• 1 onion, finely chopped
• 2 carrots, chopped into small chunks
• 4 large cloves garlic, finely chopped
• 8 portobello mushrooms, 6 chopped into larger chunks and 2 finely chopped
• 3 tablespoons tomato puree
• 2x 400 g tins green lentils, drained and rinsed
• 1 tablespoon Marmite ((or other yeast extract if GF))
• 2 tablespoons Henderson's Relish ((or half the amount of red wine vinegar, see notes))
• 400 ml vegan stock
• 2 bay leaves
• 2 teaspoons dried mixed herbs
• Salt and pepper, to taste
• 1.2 kg Maris Piper potatoes, peeled and cut into roughly 2-inch chunks
• 100 ml unsweetened plant-based milk
• 50 g plant-based butter ((plus extra to dot across the mash))
• 2 tablespoons nutritional yeast ((optional))
• 2 teaspoons wholegrain mustard ((optional))