1

Preheat oven to 450 degrees F.

2

Roll out pastry in a thin oblong shape and place on baking sheet.

3

Fry onion in butter until soft; add mushrooms and cook for a few more minutes. Remove from heat.

4

Add tuna, egg, lemon juice and capers; season with salt and pepper to taste.

5

Place mixture in the center of the pastry, dampen edges and fold over, first the top and bottom and then the sides. Press edges together well.

6

Score a couple of times across the top with a knife, brush top with milk, and bake for 15 minutes.

7

Reduce oven temperature to 400, and cook for an additional 15 minutes.

8

Let cool for a few minutes, then slice and serve.