Grease a 9x13-inch baking dish with 1 tablespoon butter and set aside. Use a sharp knife to slice the bread into ½-inch to ¾-inch thick slices.
In a large bowl, whisk the remaining melted butter, milk, cream, eggs, brown sugar, maple syrup, cinnamon, vanilla, lemon zest and salt until fully combined.
Dip each slice of bread into the milk mixture and allow to soak for 10-15 seconds. Carefully transfer them to the prepared baking dish, shingling them as you go.
Pour the remaining milk mixture over the slices. Scatter the blueberries between and on top of bread slices. Cover with foil and refrigerate for at least 1 hour, or overnight.
When ready to bake, preheat the oven to 350F. Remove and discard the foil. Sprinkle the top of the casserole with some coarse sugar, then bake for 35-45 minutes, or until golden and crispy.
Allow to cool for 10 minutes, then serve with your favorite toppings.