Grease a 9" by 13" baking pan (or one similar in size) with some butter or oil. Cut your bread into medium-sized cubes and add it to the baking dish.
To a medium bowl, add eggs, milk, honey or maple syrup, cinnamon, nutmeg (optional), salt, and lemon zest. Mix until well combined.
Pour the egg mixture over the bread. Use a spoon to mix it all up and make sure every piece of bread is well coated. Top with the blueberries. Cover the baking dish with aluminum foil and let it rest for at least 1 hour on the counter or overnight in the fridge.
Pre-heat oven to 350ºF (180ºC). Bake the casserole for 20 minutes with the foil. After that, remove the foil and bake for 20 more minutes or until golden on top and an inserted knife comes out clean.
Serve immediately and top with powdered sugar, honey, and yogurt (all optional).