Method

To make the pastry, sieve the flours into the bowl of a food processor, then cut the butter into small cubes and add it in, pulsing until the mixture looks like fine breadcrumbs. Crack the egg into a small jug or cup and beat lightly with a fork, then add it to the food processor with in a slow, steady stream, blending until the mixture comes together.

If you don’t have a processor, just sieve the flour into a large mixing bowl and gently rub in the butter with your fingertips – it helps to grate the butter rather than dice it if you are doing it this way – then add the egg and mix with your hands until you have a just-formed ball of pastry dough. 

Dust your work surface and rolling pin with a little plain flour, and roll the pastry out into a circle large enough to line a 23cm round tart tin. Push the pastry snugly against the base and up the sides of the tin, trim off any overhanging excess and then use a fork to lightly prick a few holes across the base. Put the pastry case in the fridge to chill for about 30 minutes, and towards the end of this time, preheat the oven to 200°C.

Next, take a large sheet of baking paper, crumple it up and then smooth it out again; use it to line the pastry case, then add baking beans until the case is half-full. Bake the tart case in the hot oven for 25 minutes, then remove the baking beans and paper and return the tart to the oven for a further 5-10 minutes, or until the surface is dry and lightly golden. Remove the pastry from the oven and reduce the heat to 180°C.

To make the filling, cut the trimmed onions in half and slice thinly. Place a large saucepan over a low heat and add the butter and olive oil; when the butter has melted, tip the sliced onion into the pan and cook gently for 8-10 minutes, stirring, until the onion is soft, sweet and translucent but not browned. Remove from the heat and set aside. Put the eggs in a large jug or bowl and whisk lightly with a fork. Stir in the crème fraîche and the mace, add a good pinch each of salt and pepper, then beat together with a wooden spoon until thoroughly combined. Stir in the brown crab meat.

Take the cooked onions and spread them evenly over the base of the pastry case. Add the white crab meat, spacing it evenly across the onions, then pour over the egg mixture. Grate the cheese and scatter it over the top, then cook in the centre of the oven for 25-30 minutes, or until the filling is golden and just set – a tiny bit of a wobble in the centre is OK, as the quiche will continue to set as it cools.

When you’re happy it is cooked, remove the quiche from the oven and leave to cool in the tin for 10-15 minutes. Lift it carefully out of the tin and on to a plate to serve.