This is a vegan version of one of my family’s all-time favourite dishes. I hope you will enjoy it as much as we do. You do need to make the ‘melting cheese’ for the topping in advance, but as long as you allow time for that, it’s easy. The pastry case and the red onion filling can both be made in advance too, and the tart can then be quickly assembled just before cooking. It’s delicious served with a mixed baby leaf salad and perhaps some new potatoes or creamy mash alongside.