This recipe is from Shirley McNevich's Mom's Best Recipes Vol 5. Published here with her permission.
Don't forget to check Shirley's blog.
(by Shirley McNevich)
1 heavy beer mug (clear glass) for each float
1 - 2 liter bottle A&W root beer (chilled)
1 quart premium vanilla ice cream
Place a large bowl in the sink and fill it with cool water. Dip each mug into the
water, dump out any excess water and place mugs in your freezer for 20
minutes. After 20 minutes, remove mugs from freezer and place each on its
own plate. Slowly fill each mug 2/3 full with root beer. Carefully place one
large overflowing scoop of vanilla ice cream into each mug. Slowly pour root
beer on top of ice cream in each mug until it gets close to the top of the mug
(it should fizz and spill over a bit). Place a spoon and a straw in each mug.