Ingredients :

• Canned tuna in water — Choose tuna in water rather than oil — oil unbalances the cream and makes the filling heavy. Drain it very well: leave the open can upside down over the sink for five minutes, then press with the back of a spoon in a fine strainer. Poorly drained tuna means a bottom crust that gets soggy during baking.
• Puff pastry — All-butter puff pastry makes a real difference in crunch and taste. Some low-end brands give a soft and flavorless result. Shortcrust pastry also works, but it’s less spectacular out of the oven.
• Thick crème fraîche — Thick, not liquid. Liquid cream makes the filling too fluid and it will run when sliced. If you only have liquid cream, reduce the quantity by a good third.
• Mild mustard — It completely disappears during cooking but leaves a slightly tangy background that wakes up the tuna. Avoid strong mustard here — it would overpower everything else.