Homemade soda has had a renaissance in recent years, appearing on restaurant menus across the U.S. including at Spire in Boston, Stand in New York and Wow Bao in Chicago. This might be due to health-consciousness — homemade soda typically contains less sugar than store-bought brands — or the nostalgia homemade soda stirs up. Either way, you can make cream soda at home by fermenting yeast or using devices like the Penguin Soda Maker or Sodastream Jet. The easiest and most affordable way, though, is to add homemade syrup to a fizzy base like sparkling water or seltzer water.
Pour 2 cups of seltzer water out of the bottle to create room for the soda syrup. These 2 cups of seltzer won't be used in the recipe.
Fill the liquid measuring cup with 2 cups of water. Pour 1 cup of sugar directly into the water and stir with a spoon until the sugar has dissolved. Add 1 ½ tsp. vanilla extract to the mixture and stir until it becomes a pale golden syrup.
Insert the funnel stem into the opening of the seltzer bottle. Slowly pour the syrup from the measuring cup into the mouth of the funnel.
Cap the bottle and rock it gently to mix the seltzer water and syrup.
Let the bottle sit for several minutes before trying your cream soda.