To make the shortcrust pastry, put the flour and a pinch of salt into a food processor. Add the butter and lard, and blend to the consistency of fine breadcrumbs. Transfer this to a mixing bowl. (If you don’t have a food-processor, mix the butter and lard into the flour with your fingertips in a mixing bowl.) Stir in 3-4 tablespoons of cold water – just enough to be able to bring the mixture together into a ball.
Turn out onto a lightly floured work surface and knead briefly until smooth. Roll out the pastry to a size that will line the base and sides of a 25cm/10in loose-bottomed flan tin. Press the pastry well into the crease between the base and the sides, prick the pastry base all over with a fork, and place in the fridge to chill for 30 minutes.
Preheat the oven to 190C/375F/Gas 5. Line the tart case with baking parchment and fill with baking beans. Blind bake for 15 minutes, then remove the beans and parchment and return the pastry to the oven for a further 10 minutes, or until the base is golden-brown. Remove from the oven and set aside.
To make the onion marmalade, heat a large frying pan, add the oil and butter and heat until starting to foam. Add the onions, season with salt and pepper, and cook for five minutes on a low to medium heat, stirring regularly. Stir in the sugar and caraway seeds and cover the pan, then cook for a further 10-15 minutes until the juices have come out of the onions. Taste and add more sugar if you like.
Uncover the pan and increase the heat, and continue cooking for about 20 minutes to reduce all the juices. While the juices are being reduced, preheat the oven 200C/400F/Gas 6.
When the mixture reaches the consistency of marmalade, take the pan off the heat and stir in the vinegar. Adjust the seasoning to taste.
To make the filling, beat the eggs with the cream in a jug or bowl. Mix in the onion marmalade and pour into the blind-baked pastry case. Arrange the goats’ cheese on top. Bake in the preheated oven for 30-35 minutes, or until set and lightly browned on top.
Remove from the oven and leave to cool slightly. Garnish with a scattering of tarragon and coriander leaves if you like.