Cooking butter with sugar causes milk solids to caramelize, giving butterscotch sauce its delicious flavor.
- 8 tbsp. unsalted butter (like Meggle Unsalted Alpine butter)
- 2 tbsp. light corn syrup
- 3⁄4 cup granulated sugar
- 1⁄4 cup light brown sugar
- 1⁄3 cup heavy cream
- 1 tsp. dark rum
- 1 tsp. vanilla extract
- 1⁄2 tsp. fine salt
- 1⁄2 tsp. fresh lemon juice
Heat butter, corn syrup, and 1⁄4 cup water in a medium saucepan over medium-low heat, stirring constantly, until butter has melted.
Stir in granulated sugar and brown sugar; scrape down sides of pan with a rubber spatula. Bring mixture to a boil over medium heat, without stirring. Cook until light brown and a candy thermometer inserted in sauce reads 245°, 6–8 minutes.
Remove from heat; carefully add heavy cream, rum, vanilla extract, salt, and lemon juice; stir to combine. Let sauce cool to room temperature. Serve over ice cream.