Combine 1 cup heavy cream, chocolate and peanut butter in a small saucepan. Warm mixture over medium heat, whisking, until chocolate is melted and mixture is smooth, about 5 minutes. Set aside to cool slightly.
Combine remaining 1/2 cup heavy cream and confectioners' sugar in a medium bowl and use an electric mixer or a whisk to whip until cream just holds stiff peaks.
Place 2 small scoops of ice cream (about 2 Tbsp. each) in each of 4 sundae or parfait glasses and sprinkle each with about 1 Tbsp. chocolate-covered raisins. Repeat with 2 more scoops of ice cream and remaining chocolate-covered raisins. Drizzle about 3 Tbsp. warm chocolate-peanut butter sauce over each sundae and then top off with a dollop of whipped cream. Serve immediately.
