Preheat the oven to 200°C, gas mark 6
Heat the olive oil in a saucepan, add the onion and leek and cook for about 5 minutes or until the vegetables have softened.
Add the crab, creme fraiche, lemon juice and zest, cheese and tarragon and heat gently for a few minutes until everything is combined and warmed through.
Season with salt and pepper, taste and adjust the seasoning as required.
Unroll the puff pastry sheet and cut 12 discs out of the pastry using an 8cm cookie cutter.
Add each of the pastry discs to a 12 hole bun tray, pressing the pastry down into the holes. Prick the bottom of the pastry a few times with a fork, this allows the steam to escape from the pastry as it’s baking and stops it from puffing up in the oven.
Divide the crab and cheese mixture between each of the pastry cases and brush the edges of the pastry with a little olive oil.
Bake in the centre of the oven for 15-20 minutes, or until the pastry is golden brown and cooked through.
While the tarts are cooking make the salad by slicing the fennel very thinly (you could use a mandolin for this but a sharp knife works just as well and is less dangerous). Add to a bowl with the rocket, olive oil, lemon juice and seasoning. Toss the salad to ensure everything is combined.
To serve, add the tartlets to a plate and serve the salad alongside. This would work as a starter for four people or a light meal for three.