BUTTERSCOTCH SAUCE
1 cup packed light brown sugar
1/2 cup heavy cream
1/4 cup light corn syrup
dash of salt
4 tbsp unsalted butter
1-1/2 tsp vanilla extract
1/4 tsp lemon juice
In a sauce pan, stir together the brown sugar, cream, corn syrup and salt; heat to a simmer, and cook until the sugar is melted. Remove from the heat, stir in the butter until it melts, and cool for 5 minutes. Stir in the vanilla extract and lemon juice. Makes about 2 cups, and can be used warm or cool.
BUTTERSCOTCH SWIRL ICE CREAM
1 recipe French Vanilla ice cream
1 recipe butterscotch sauce
Make the ice cream. When it's soft-set, drizzle the fully cooled butterscotch sauce over the ice cream and stir in. Note: this would work best with 3 hands, so you'll need a helper. Maybe it could be put in during the last minute that the ice cream processor is doing its thing, but I didn't try it. Freeze until the ice cream's firm.
Of course, you can drizzle still more butterscotch sauce over your ice cream for extra flavor!