Preheat the oven to 425 degrees F. Spray four 6-ounce ovenproof ramekins with baking spray and place on a baking sheet.
Microwave the butterscotch chips and butter in a large microwave-safe bowl until the butter is melted, about 1 minute. Whisk until smooth and the butterscotch has melted. Stir in the sugar until well blended. Whisk in the whole eggs and yolks, then add the vanilla. Stir in the flour. Divide the mixture among the prepared ramekins.
Bake until the sides of the cakes are firm and the centers are soft, 13 to 15 minutes. Let stand 1 minute. Invert onto individual plates while warm. Serve with chocolate ice cream on top.