Place the fruit in a pan. Remove the stems from the redcurrants (if using) with a fork, pour the sugar over the fruit and stir gently to mix together.
If you have time, cover the pan with a tea towel or cling film and leave for 3-5 hours (or overnight) to get the juices running. Place the pan over a moderate heat and bring gently up to the boil.
While the fruit is simmering, cut the bread into thin slices and remove the crusts.
When the juices are beginning to flow, raise the heat slightly and simmer for about 2-3 minutes. Then turn off the heat and stir in the cassis or blackcurrant cordial.
Cut a round out of one slice of bread to fit the bottom of the bowl, then cut the remaining slices into triangular wedges.
Dip one side of the bread circle into the juices in the pan containing the fruit, then place the circle in the bottom of the pudding basin, juice-side down. Do the same with the bread triangles, dipping one side of the bread into the juices before placing them around the edge of the bowl, with the dipped side facing outwards. The tips of the bread triangles will be sticking up from the top of the bowl at this stage.
Once the bowl is completely lined with the juice-soaked bread (be sure to plug any gaps with small pieces of bread if necessary), spoon all of the fruit and its juices into the pudding basin. Trim the tips of bread from around the edge. Cover the top of the fruit with more wedges of bread. Place the pudding basin on a plate to collect any juices.
Find a saucer that fits neatly inside the bowl. Place it on top to cover the upper layer of bread, then weigh the saucer down with weights - bags of rice, tins of baked beans, or whatever comes to hand. Let it cool, then place in the fridge overnight.
The next day, remove the weights and the saucer. Run a thin blade around the edges, then invert the basin onto a shallow serving plate.
Turn the pudding out, cut into thick slices and serve the summer pudding with cream.