Combine the ale, half of the cream, soda, butterscotch, vanilla extract, and vinegar in a small saucepan over medium heat. Stir occasionally to prevent the sugar from burning the on bottom.

Bring the mixture just up to a simmer.

Meanwhile, whip the rest of the cream to soft peaks. You can sweeten it slightly with sugar but I feel the drink it sweet enough already.

To serve, pour the butterbeer in mugs and top with lightly whipped cream.