Use a skewer to prick the lemons all over.
Finely dice the butter and put it back in the fridge.
Mix the suet into the flour, then add the milk.
Knead until you have a dough.
Divide it into 2 balls, one using ⅓ of the mixture and the other using ⅔ of the mixture.
Sprinkle flour over a clean worktop and roll out the bigger ball.
Use it to line the bottom and sides of a greased 1½ quart (1½ litre) pudding basin.
Add half the sugar and half the chopped butter pieces.
Add the currants if using.
Put the whole lemons on top.
Now add the remaining butter and sugar.
Roll out the other dough ball and use it to top the pudding.
Brush the edges with water and press to seal.
Wrap the pudding in one large piece of baking paper.
Tie under the basin rim with kitchen string to hold it down.
Make a loose 'handle' over the top of the pudding using the string, then cut and tie.
Trim off excess baking paper.
Put the basin in a pan.
Pour hot water into the pan about ⅔ of the way up.
Cover and simmer for 3½ hours.
You might need to top up the water during cooking.
Let the pudding rest for 10 minutes.
Turn it out on to a serving dish.
Serve the Sussex pond pudding hot in wedges, ensuring each person gets some of the lemon.