Preheat the oven to 350°F (175°C). Grease a 9×13-inch baking dish with butter or nonstick spray.

Cook the bacon in a skillet over medium heat until crisp. Drain on paper towels, then crumble or chop into bite-size pieces.

In a medium bowl, whisk the eggs and milk until smooth. Season with a pinch of salt and several grinds of black pepper.

Spread the bread cubes evenly in the prepared dish. Scatter the crumbled bacon over the bread. Sprinkle the shredded cheese across the top and add any optional veggies.

Pour the egg-and-milk mixture slowly and evenly over the layers. Press gently so the bread soaks up the custard. Let the casserole sit 5–10 minutes to absorb.

Bake for 30–40 minutes, until the center is set and the top is golden. A toothpick inserted in the center should come out mostly clean. If you prefer, the internal temperature should reach about 160°F for a fully set egg custard.

Remove from the oven and let cool for a few minutes before slicing. Serve warm.