Place the bread cubes and blackberries in a 9X13 baking dish and toss to distribute the blackberries evenly.
In a large bowl, whisk the remaining ingredients together into a frothy custard base.
Pour the custard over the bread cubes. Cover and refrigerate for at least 2 hours.
Preheat the oven to 350 degrees F. Bake uncovered for 1 hour and 15 minutes, until golden and bubbly. The bread pudding should still be a little jiggly in the middle. All it to cool for 20 minutes before serving. (If the top starts to get too dark, place a piece of loose foil over it while baking.)