Grease a 9 x 13 x 2-inch oval baking dish with the butter and set aside. In a large bowl, whisk together the eggs, half-and-half, 1/3 cup of granulated sugar, the brown sugar, vanilla, orange zest, and salt.
Spread half of the diced bread in the prepared baking dish. Sprinkle on the raspberries in one layer. Top with the rest of the bread and pour on the egg mixture, pressing down lightly to moisten the bread. Sprinkle with the remaining 2 tablespoons of sugar, cover with plastic wrap, and refrigerate for 1 hour.
Preheat the oven to 350 degrees. Place the baking dish on a sheet pan and bake it for 60 to 70 minutes, until the custard is set and the top is puffed and browned. Check after 45 minutes; if the top is getting too browned, cover it lightly with aluminum foil. Cool for 10 minutes, sprinkle with confectioners' sugar, dust with extra orange zest, and serve warm with maple syrup.