Mash Topped Vegetable Pie

Name: Mash Topped Vegetable Pie
Prep time: 15 min
Cook time: 40 min
Total time: 55 min
Cuisine: British, European
Ingredients: 4 carrots, sliced thickly; 1 cauliflower, cut into florets and then halved; 340g tin/2 cups sweetcorn; 1kg potatoes, peeled and quartered; 5 tbsp olive oil (for the mash); 2 tsp olive oil (for the mushrooms); 4 large flat mushrooms, sliced; 60g butter (dairy free spread) for the sauce; 7 tbsp plain flour; 300ml milk (unsweetened soy milk); 120g mature cheddar grated (vegan cheddar & vegan parmesan); ½ tsp English mustard powder (optional); a good grinding of salt and pepper