You will also need flour.

Turn oven to 180deg C

Spread a thin layer of flour over your working area to stop the pastry sticking,
Cut the pastry into two lumps, one about 1.5 times the size of the other.

Roll the big lump out (you can use a wine bottle or milk bottle if you don't have a rolling pin) to thinner than you think you can possibly need it - about half the thickness of the pastry you have in mind (it expands on cooking). If it all goes wrong, just roll it back into a ball and start again - pastry is forgiving stuff.

Find an over proof dish of the right size for the piece of pastry you have rolled out to cover its base and sides. If the edges are irregular, you can break off pieces that are hanging over the edge and use them to patch any gaps. Finally, use a knife to trim the top edge.

Fill with blackberries (they cook quickly so you shouldn't need to pre-cook them) and a bit of sugar if you think you need it.

Roll out the other piece of pastry and put it on top. Trim the edges, and cut two inch-long slits in the middle "to let the steam out" - I don't know whether this is necessary but it's traditional. Put it in the oven, preferably standing the dish on a baking sheet in case of any drips.

Start checking after 15 mins, and take it out when the top looks dry and is just beginning to get a golden tinge.


Other easy alternatives:

1) Blackberry crumble: Take some flour and half as much by weight of butter or marg. Use your finger tips to squash the fat into the flour, breaking it up so that eventually it looks "like breadcrumbs". Mix in some sugar - not more than a quarter of the weight of the flour, probably less. Scatter it on top of the blackberries and cook as for pie.

2) Blackberry sponge: Take equal weight of eggs, marg, sugar and flour. Use a beater to mix the sugar and marg until it looks paler and fluffier, add the eggs and stir in, add the flour and stir in. Spread on top of the blackberries, cook at 180 deg C, when it looks golden brown, test by pressing with your finger. If it leaves a dent and doesn't bounce back up, you need to cook it a bit longer.

3) You can stretch the blackberries without adversely affecting the taste by adding apples. To be in the safe side, you might want to pre-cook these a bit, as they taste better when soft and pureed.