Vigorously whisk eggs, egg yolks, salt, white sugar, and brown sugar together in a large bowl until mixture turns light and frothy, about 1 minute. Add vanilla, cinnamon, lemon zest, milk, and cream; whisk to combine. Toss in bread slices and press down until they start to soften and are submerged. Let sit, pressing down occasionally with a spatula, until custard has been absorbed, about 20 minutes.
Preheat the oven to 375 degrees F (190 degrees C). Brush 2 tablespoons melted butter in the bottom and sides of a 9×13-inch baking dish.
Grab a few intact bread slices from the top of the bowl if possible and set aside. Transfer 1/2 of the remaining soaked bread into the prepared baking dish. Don’t worry if it’s falling apart, it should be; if not, break it up into pieces. Add blueberries and spread with your fingers to press them down into the bread. Add remaining bread pieces in an even layer, then top with the reserved slices. Pour any remaining custard batter over top and brush with remaining melted butter.
Transfer bread pudding onto a baking sheet and place in the center of the preheated oven. Bake until puffed and golden brown, about 1 hour. Let sit for at least 20 to 30 minutes before serving.
Serve slightly warm or at room temperature.