Preparation

To make the butterscotch crunch:

• Spray a 13×9-inch baking pan or Pyrex dish with nonstick spray or grease it very lightly. In a medium, heavy-based saucepan, combine the cream, butter, brown sugar, and salt. Bring to a boil over medium-high heat, stirring often. When big bubbles start to form, check the mixture with a candy thermometer. As soon as it reaches 285°F, remove it from the heat and carefully stir in the whisky and vanilla. Carefully pour the mixture into the prepared pan, spreading it with an oiled spatula. Let cool. Break the cooled candy into chunks and pulse the chunks in a food processor (in batches if necessary) until the pieces are the size of corn kernels. If you create a lot of powder, you might want to sift the crunch before adding it to the ice cream.

To make the ice cream:

• In a medium, heavy-based saucepan, combine the milk and vanilla bean and bring to a simmer over medium heat. Fill a large bowl with ice.
• Meanwhile, in a medium bowl, whisk the brown sugar, egg yolks, and vanilla extract until combined. Slowly pour some of the hot cream mixture into the yolk mixture, stirring to temper it. Return this mixture to the pan and cook over medium heat, stirring until it’s slightly thickened and coats the back of a wooden spoon.
• Pour the mixture into a clean medium bowl and nestle it into the bowl of ice; stir the mixture to cool it and then refrigerate until very cold. Strain the mixture and freeze it in an ice-cream maker following the manufacturer’s directions. When almost completely frozen, swirl in the butterscotch crunch: put half of the ice cream in a chilled stainless-steel bowl, sprinkle half of the crunch on top, and swirl with a butter knife. Top with the remaining ice cream and crunch and swirl again. Cover the ice cream tightly with plastic wrap and freeze.