Preheat oven to 400 degrees F (200 degrees C). Grease cookie sheets.
Beat in the eggs one at a time, then stir in the vanilla.
In a mixing bowl, mix the butter, sugars, egg mixture with a wooden spoon until creamy and fluffy.
Sift flour in it in 2 batches. Stir in the orange zest until blended and smooth and set it aside for 1 hour.
Divide dough into 22 walnut-size balls and roll them using rolling pin.
Transfer them to the cookie sheet and space cookies 1 1/2-inches apart.
Bake for 15 minutes until golden.
Remove from cookie sheets to cool on wire racks about 10 minutes.
Meanwhile, mix the icing sugar with enough orange juice to make a thick, runny icing.
Dip each biscuit half into the icing, then straight into the sprinkles.
Dry on a wire rack.