How to cook
Cut the onion into medium sized pieces and stew it until it softens.
Salt the onion and add the tuna fillet.
Season with black pepper and add the heavy cream.
Open up the puff pastry and pour the filling in the middle of it, lengthwise.
Make strip like cuts on both sides of the dough of approximately 2.4″ (6 cm) and a width of approximately 1.2″ (3 cm).
Fold the filling along with the dough by twisting it, alternating the strips on both sides to make something like a braid with the puff pastry.
If you find it difficult, just roll it up on both sides and pinch the top. You can make holes with a toothpick.
Beat an egg and with a brush spread the mixture on the wrapped up savory pie.
Bake at 430°F (220 degrees) until golden.
A very tasty puff pastry fish pie!