Trim crusts off bread. Cut loaf crosswise into 3/4-inch-thick slices. Arrange 8 to 10 slices diagonally in a buttered 8-inch square pan, overlapping to fit. If needed, lean the slices over so they don't extend above sides of pan. If bread is too wide, trim it.
In a bowl, whisk eggs, half-and-half, sugar, vanilla, and nutmeg until well blended. Slowly pour liquid over bread. Let stand until bread feels soft all over and most of the liquid is absorbed, 30 to 40 minutes; occasionally tip pan and spoon liquid over the top.
Bake in a 350° oven until custard no longer flows in center when pan is gently tilted, about 30 minutes.
If pudding is pale, broil 3 to 4 inches from heat until golden and crusty, 3 to 4 minutes. Serve warm or cool.