30 minutes, plus overnight for the loaf to stand. Three tricks for perfect results: Use day-old bread, cut each bread cube to include some crust, and soak the skewers.
Soak 12 wooden skewers (10 to 12 in.) in water to cover for 20 minutes; drain. Meanwhile, heat a grill to medium (350°).
Cut enough bread into 1-in. chunks, including some crust on each, to make 2 qts; save extra for other uses.
Whisk milk, eggs, and vanilla in a large bowl to blend. Mix in bread to coat, then thread onto skewers.
Oil cooking grate, using tongs and an oiled wad of paper towels. Grill skewers, covered, until browned, turning once, 3 to 4 minutes.
Serve with butter and syrup and dust with powdered sugar if you like.
Note: Nutritional analysis is per serving.