Preheat the oven to 180°C/Gas 4. Make the shortcrust pastry in the normal way, or with 50:50 wholewheat/plain flour. Bake blind and dry out in the oven.
For the middle: melt the butter with the olive oil in a large, heavy-bottomed frying pan, then throw in the leeks and leek tops, season and sauté gently until they begin to wilt and soften.
Remove from the heat and add the fresh herbs.Whisk together the cream, eggs, seasoning and Gruyère. Scrape the leeks into the cream.
Slice the goat’s cheese and arrange around the edge of the tart, scrape in the leeky custard and bake for 35–40 minutes or until set and browned.