Step 1Trim the crusts from the bread and if it has not been sliced, cut it in roughly one-third-inch slices. Stack the slices and cut them in half diagonally to make triangles.
Step 2Line a 6-cup mold or bowl with plastic wrap, fitting the wrap tightly into the corners. Make sure you have a plate small enough to fit just inside the rim of the bowl. If not, cut a stiff cardboard circle that will fit and wrap it in aluminum foil (to be used in Step 6).
Step 3Piece together the bread slices in a single layer so they completely line the bowl. There should be no gaps, but the fit doesn't have to be exact -- wherever the bread overlaps, simply press the edges together tightly. Trim the bread where it comes over the top of the bowl.
Step 4Cut a shallow "X" in the base of each peach, and then dunk the peaches in rapidly boiling water until you see the peel start to come loose at the cut -- about 20 seconds to 1 minute, depending on the ripeness of the fruit. Remove the peaches from the water and rinse under cold running water. The peels should slip off easily; if they don't, return the fruit briefly to the boiling water. Pit the peaches and cut them into chunks.
Step 5Combine the peaches, blackberries and sugar in a saucepan and warm over medium heat. Cook just until the fruit begins to soften and release its juice, 3 or 4 minutes. Stir in the brandy.
Step 6Spoon the fruit into the bowl; there should be enough that it mounds a little above the lip. Place a sheet of plastic wrap loosely across the top, then place the plate or cardboard circle on top. Press gently and stack a heavy can on top (tomatoes work great). Refrigerate at least 12 hours.
Step 7When ready to serve, remove the plate and the top layer of plastic wrap. Place a serving plate on top of the bowl or mold and invert the bowl so the pudding will unmold onto the serving plate. If the pudding resists unmolding, hold the plastic wrap and jiggle gently until it does unmold cleanly. Remove the plastic wrap lining.
Step 8Serve immediately with lightly sweetened whipped cream or yogurt.