Step 1Line an 8- to 9-inch square baking dish with plastic wrap, leaving enough overhang to cover the top of the pudding. Line the bottom of the prepared pan with a tight-fitting layer of bread, trimming to fit.
Step 2In a large nonreactive skillet, heat the berries and optional currants with the sugar over medium heat just until they give off their juices. Remove from heat and sprinkle with the kirsch. Spoon half of the berry mixture over the bread. Top with a second layer of bread, then the remaining berry mixture, and a final layer of bread. Cover with the overhanging plastic wrap. Place another baking dish of the same size on top of the pudding, and weight with a few heavy cans. Place on a baking sheet to catch any juices, and refrigerate overnight.
Step 3Unwrap the top of the pudding. Invert the pudding onto a serving platter (with a lip to hold the juices) and unmold, pulling off the plastic wrap. Cut into 8 to 10 squares and transfer to dessert plates. Serve with a dollop of whipped cream.