Prep the pan: Heat oven to 350°F (175°C). Spray a 12-cup muffin tin well or use liners.

Cube the bread: Cut bread into 1/2–1-inch cubes. If it’s fresh, toast on a sheet pan at 300°F (150°C) for 8–10 minutes to dry it out slightly.

Make the custard: In a large bowl, whisk eggs, milk, Greek yogurt, protein powder, maple syrup, vanilla, cinnamon, and salt until smooth. Break up any protein powder clumps.

Toss it together: Add bread cubes to the bowl and gently fold until every piece is coated. Let it sit 5–10 minutes so the bread absorbs the mixture. Stir once more. Fold in any add-ins.

Fill the tin: Divide the mixture evenly among cups, pressing lightly to compact. Sprinkle with turbinado sugar or nuts if using.

Bake: Bake 22–28 minutes, until tops are golden and the centers are set. A toothpick should come out with a few moist crumbs, not wet custard.

Cool: Let muffins rest 5–10 minutes, then loosen edges with a knife and transfer to a rack. They firm up as they cool.

Serve: Enjoy warm as is, or add a drizzle of syrup, a dollop of yogurt, or fresh berries.