Grease a 9×13 baking dish. Spread half the bread cubes in the dish.Sprinkle blueberries evenly. Add remaining bread on top.
Whisk eggs, milk, cream, sugar, vanilla, cinnamon, and lemon zest. Pour evenly over bread. Press gently so all bread absorbs liquid.
Cover and refrigerate at least 4 hours or overnight.
Mix brown sugar, flour, and cinnamon. Cut in butter until crumbly. Sprinkle over casserole before baking.
Preheat oven to 350°F (175°C). Bake uncovered for 45–55 minutes, until golden and set.
Serve with whipping cream and more blueberries.