Preheat oven to 350° F. Butter a 9"x13" baking pan.
In a large bowl, whisk together eggs, half & half, granulated sugar, brown sugar, vanilla, orange zest and salt.
Layer half the diced bread in prepared baking pan. Spread the blueberries in a single layer. Top with remaining bread. Pour the egg mixture over blueberries and press down to make sure all the bread is soaked. Sprinkle with the remaining 2 tablespoon of sugar and cover with plastic wrap. Refrigerate for at least 1 hour or overnight.
Place rack in middle of oven and preheat to 350° F.
Put the baking pan on a sheet pan and bake for 60-70 minutes, until the custard is set. The top should be puffy and golden brown. Check after 45 minutes. If it's getting too brown, cover lightly with aluminum foil.
Once done, remove from oven and cool for 10 minutes. Sprinkle with confectioners' sugar and dust with remaining orange zest.
Serve with warm maple syrup.
Notes
Best to prepare this casserole the night before, and enjoy an easy morning.