Tear bread into bite-sized pieces, and place in a greased 9"x13" baking dish.
In a large mixing bowl, whisk together eggs, eggnog, vanilla, cinnamon, nutmeg, and sugar.
Pour egg mixture over bread.
Cover with foil and press down gently so the bread will soak up all the egg mixture.
Refrigerate overnight or minimally 3-4 hours.
Preheat oven to 350°F.
For the topping: Right before you bake, whisk together the flour, brown sugar, cinnamon, and nutmeg for the topping in a medium mixing bowl. Add butter and cut in with a pastry blender or fork, until the clumps are pea-sized.
Sprinkle topping onto the casserole.
Bake at 350°F for about 45 minutes, or until cooked through.
Just before serving, mix all of the glaze ingredients in a medium mixing bowl and whisk to combine. Drizzle over entire casserole or individual slices before serving.