Roast tomato and harissa tart with an oat crust recipe Save Follow Lucy grew up with this recipe, as it is a favourite of her mumâs. It was originally a Jane Grigson recipe, a cook her mother often turned to for inspiration. Thereâs no need to roll out this dough â just press it straight into the tin. Prep time: 15 minutes | 125g porridge oats 125g fat (we use a half-and-half mixture of butter and Trex, but you can use all butter) 1 large egg, beaten 1 x 400g tin chopped tomatoes 1 large egg 1 heaped tbsp grated Parmesan 60g cheddar, grated, plus extra for the top (optional)