1. Lightly butter a 9- by 13-inch pan. Lay baguette slices on a cut side in a single layer in pan, squeezing if needed to make them fit. In a blender or in a bowl with a whisk, whirl or beat eggs, half-and-half, milk, nutmeg, cinnamon, and vanilla to blend well. Pour egg mixture over bread to moisten evenly. Cover and refrigerate at least 8 or up to 24 hours.
2. In a 1- to 2-quart pan over medium heat, stir 1/4 cup butter with brown sugar, corn syrup, and pecans until butter melts. Uncover bread mixture and spread slices evenly with the butter mixture, using all of it.
3. Bake, uncovered, in a 350° oven until topping is browned and bubbly, about 45 minutes. Scoop portions into bowls.