Line a bowl (I used a 1 1/2 quart pyrex bowl) with sheets of plastic wrap so that you'll be able to easily unmold the pudding.
Trim the crusts of the bread slices and butter them on one side. Line the mold with the bread slices, cutting to fit all the gaps, buttered side toward the bowl.
In a saucepan, add berries and sugar and bring to a simmer. Cook gently for about 10 minutes, just until sugar dissolves and berries release their juices.
Fill the mold with the berries all the way to the top. (The pudding will be pressed and shrink a bit)
Top the berries with more buttered bread slices until the entire pudding is encased.
Cover with plastic wrap, and a plate that's slightly smaller than the bowl. Weigh the plate down with some cans and refrigerate overnight.
Whip the cream until peaks form with sugar and vanilla.
Cover the whole pudding with the whipped cream. Finish with berries and mint.
To serve, just scoop it like a trifle or ice cream.
Serves about 10 to 12 depending on how big your portions are. I usually make it when I'm going to have a big crowd.