NOTE: This challah takes a long time to make, with all the rising. Plan to start early in the morning.
Mix water and yeast in a very large bowl. Add 3 cups flour and 1 cup sugar. Stir with a fork; let rise 1/2 hour in a warm place.
Meanwhile, put the dried mango in a small bowl and add the orange liquor. Let them soak. In another bowl, measure 5 cups of flour, the salt, and the remaining sugar. Cut in the margarine with a pastry blender or knife until the mixture resembles coarse meal. After the yeast mixture has sat for 1/2 hour, beat four eggs and add them in. (The mixture will deflate.) Add flour-margarine mixture to yeast mixture and work until combined. Drain the mango peaces and add them to the dough along with 2 tsp of the soaking liquid. Add up to 2 cups flour if the dough is sticky. Turn onto a floured counter or board and knead well. Cover with a cloth and allow to rise about two hours, until doubled.
Punch down, knead for a minute or two, then let rest five minutes. Shape the dough into a round challah (or two smaller round challot, or a bird, or whatever Rosh Hashanah shape you prefer) on a lightly oiled cookie sheet, or a large round cake pan. Cover, put in a warm place and let rise at least 3 hours. (Depending on how warm your rising place is, you can let it go up to 5 hours.)
Heat oven to 350 degrees F. Beat the remaining egg, add a tablespoon of warm water, and mix to make egg wash. Brush the bread with the wash and sprinkle the top liberally with the almonds. Bake for about 45 minutes.
6 to 8 servings