Butter extract and chocolate shards are sold at baking supply stores.
Prep Time 10 minutes
Cook Time 3 minutes
Total Time 13 minutes
Make a simply syrup. Boil together the light brown sugar with a cup of water until the sugar is dissolved. Cool. Stir in the vanilla extract and half of the butter extract. Transfer the syrup to a jar with a screw-type cap and chill for a few hours.
In a pitcher, stir together 3/4 cup of the chilled syrup, all of the soda water, rum and the remaining butter extract.
Stir the milk into the whipped cream to thin it a bit.
Divide the whipped cream among three glasses.
Pour the rum-syrup mixture over the cream, leaving enough space for the ice cream topping.
Top each glass with a scoop of vanilla ice cream. Sprinkle in some chocolate shards.
Serve the butterbeer at once.