In a medium saucepan, melt the butter over medium heat. Add the sugar, cream and salt and whisk until combined. Bring to a boil, then reduce the heat and simmer, stirring occasionally, until smooth and thickened, 5 to 10 minutes. Remove from the heat and stir in the vanilla bean paste; the sauce will thicken as it cools.
Scoop vanilla ice cream on top of the blondies, then top with the butterscotch sauce, cashews and whipped cream.