Place the puff pastry in a tart pan with high sides and prick the bottom with a fork.

Cut the leeks into small pieces and cook them in salted water for 5-8 minutes. Meanwhile, spread the canned tuna (drained) over the pastry.

Make the custard by mixing 1 egg, 3/4 cup heavy cream (about 200 ml), 1/3 cup milk (about 100 ml), and season well with salt and pepper.

Spread the cooked leeks over the tuna, then pour the custard mixture on top.

Bake in the oven for about 30 minutes, then enjoy!