Grease the bottom and sides of a 9-by-13-inch baking dish with butter. Slice the bread into 3/4-to-1-inch-thick slices. If your bread is very fresh, lightly toast the slices before assembling. Tile all the bread in the dish, each slice overlapping the next. Scatter the blueberries over the bread, letting some fall to the bottom of the dish.
Whisk the eggs, milk, 120ml cream, 66g cup granulated sugar, almond extract and salt in a medium bowl until the sugar is dissolved. Pour over the bread and berries and press gently to help the bread start soaking in the egg mixture. Cut the 2 tablespoons butter into small pieces and dot over the top of the casserole. Cover with plastic wrap and let stand in the refrigerator 8 hours or overnight.
Preheat the oven to 170°C. Remove and discard the plastic wrap. Bake the casserole until golden brown and set in the center, 45 to 50 minutes, tenting with foil if the bread starts to become too dark. Let stand 10 minutes. Dust with icing sugar if desired.
While the casserole bakes, toss the strawberries and raspberries with 1 tablespoon granulated sugar in a medium bowl and let stand until juicy.
Before serving, whip the remaining cream with the remaining 1 tablespoon granulated sugar and vanilla until soft peaks form. Serve the casserole with a dollop of whipped cream and a generous spoonful of the berries with their juices.