Butter a 9x13-inch baking dish generously. Arrange the bread cubes in the dish in an even layer.
In a large mixing bowl, whisk together the eggs, milk, heavy cream, granulated sugar, vanilla extract, lemon zest, lemon juice, and salt until smooth and well combined.
Pour the custard mixture evenly over the bread cubes, pressing down gently with a spatula to ensure all pieces are submerged. Let stand for 20-30 minutes at room temperature, pressing down occasionally.
Preheat your oven to 350°F (175°C) while the bread soaks.
Toss the blueberries with 1 teaspoon of flour, then gently fold them into the soaked bread mixture, distributing them evenly throughout.
Drizzle the melted butter over the top and sprinkle with turbinado sugar for a golden, crunchy crust.
Bake for 45-50 minutes until the top is golden brown and puffed, and a knife inserted in the center comes out mostly clean with just a few moist crumbs.
Remove from the oven and let cool for 10-15 minutes before serving. The pudding will set as it cools and become easier to slice.
