To make the pastry, mix together the butter and flour to make a breadcrumb texture. You can do this by hand with a knife and your fingers, or use a mixer.
Slowly add the water, you may not need all of it, mixing the butter, flour and water together until you have a dough.
Wrap the pastry in cling film and chill for 30 minutes.
Remove the pastry from the fridge. Dust a little flour over your worktop and a rolling pin. Roll the pastry out so that it is just larger than the tin, allowing enough to go up the sides.
Lay the pastry into the tin and push it gently into the base and sides. Prick the base all over with a fork then put back into the fridge for another 30 minutes.
While waiting for the pastry, make the frangipane filling.
Beat the sugar, butter, almonds and eggs to make a paste. Add most of the blackcurrants to the almond mix and stir them in. Cover and chill the mix in the fridge for 20 minutes.
Preheat an oven to 190C.
Remove the pastry case from the fridge and line it with greaseproof paper. Fill the tin with baking beans (see below) and put in the oven to blind bake for 15 minutes.
Take the tart case out of the oven and carefully remove the baking beans and greaseproof paper.
Spread the almond mixture into the tart case and put the tart back in the oven for 25 minutes.
Leave to cool slightly before removing from the tin. Scatter the remaining blackcurrants over the top of the tart. This tart is delicious served warm and it's also good cold.