Grease a 9x13” baking dish. Spread half the bread cubes in the dish, top with 2/3 of the blueberries and followed by the remaining bread cubes.
Whisk together the eggs, milk, cream, vanilla, maple orange sugar, white sugar, lemon zest and sea salt. Pour over the bread cubes and cover with plastic wrap. Refrigerate overnight.
Preheat the oven to 350F. Before baking, drizzle the top of the casserole with olive oil. Bake for 45 minutes until slightly puffed and golden. Remove from the oven and let cool for 10 minutes before cutting.
While the casserole is cooling, combine the blueberries, balsamic vinegar, water and cornstarch in a saucepan. Bring to a boil and reduce to a simmer, stirring until the blueberries start to burst.
Serve the casserole with a drizzle of the balsamic syrup on top.