Begin by preparing the rhubarb. Wash the stalks thoroughly, remove any leaves, and chop them into small pieces. Place the chopped rhubarb in a saucepan and add the sugar and lemon juice. Cook over medium heat until the rhubarb breaks down and releases its juices, which will thicken slightly to form a syrup. Stir occasionally to prevent burning and ensure even cooking.

Once the rhubarb has cooked down into a soft, syrupy mixture, remove the saucepan from heat. While it cools, prepare the bread by slicing it thinly. You can use a serrated knife for this to get even, delicate slices. If you prefer, you can lightly butter the bread, but it’s not necessary.

Take a pudding basin or a deep bowl and begin layering the bread slices. Dip each slice into the cooked rhubarb mixture, ensuring it is well soaked but not too soggy. Layer the soaked bread at the bottom of the bowl, and continue layering until the dish is full, ending with a layer of rhubarb on top. Press down gently to compact the layers and ensure even soaking.

Once your pudding is assembled, cover the top with a layer of plastic wrap or parchment paper. Place a weight or something heavy on top to help the pudding compact further, allowing it to set. Let it chill in the refrigerator for at least an hour or, ideally, overnight for the best flavor absorption.

When ready to serve, turn the pudding out onto a serving plate, removing the plastic wrap or parchment paper. You can warm it slightly in the oven if you prefer it served warm, or enjoy it chilled. Serve with golden custard sauce or whipped cream on the side.