Combine 4 cups hot coffee, 1/4 cup sugar, and 1/2 teaspoon lemon zest in a large mixing bowl. Coffee should be hot (as opposed to cold or room temperature) to ensure that sugar dissolves completely. Whisk ingredients together until well combined. (For a grown-up treat, add a shot of coffee liquor to your mixture before freezing).

Pour coffee mixture into a medium baking sheet or brownie pan. A pan with raised sides will help prevent spills.

Place in freezer for 30 minutes, or until crystals begin to form. As soon as the coffee starts to freeze, use a fork to break up the crystals (carefully, so as not to scratch your metal pan). Return to freezer.

Repeat this process every 15-20 minutes, continually breaking up the crystals that forms as your mixture freezes. As you do this, you'll see that your mixture takes on a slushy, almost snow-like consistency.

Do this until your mixture is completely "dry" and no more liquid remains. Your granita will be light and fluffy, easily scooped up with a spoon.

Scoop granita into a parfait glass, about 1/3 full. Layer with 1/2 cup whipped topping. Add another layer of granita and finish with more whipped topping and additional lemon zest for garnish.