Make butterscotch sauce: In a small saucepan, combine 1/3 cup cream, butter, brown sugar, and corn syrup. Bring to a boil over high heat; cook, stirring occasionally, until sugar has dissolved, 2 to 3 minutes. Let cool to room temperature. Sauce can also be made up to 1 week ahead; cover and refrigerate in an airtight container.
If sauce is refrigerated, place in microwave, before serving, for 30 seconds; stir. If still too thick, microwave for 15 seconds more, and stir again.
Whip the cream: In a large bowl, whisk remaining 2/3 cup cream and granulated sugar until soft peaks form.
Assemble: In each of eight shallow dishes, arrange 2 banana halves lengthwise. Place 2 scoops ice cream on bananas. Top with butterscotch sauce, whipped cream, and, if desired, peanuts and a cherry.