If desired, lightly line the slow cooker insert with strips of parchment paper, leaving a little overhang at the sides. Arrange 6 unwrapped frozen ice cream sandwiches in an even layer across the bottom of the slow cooker.

Spoon about half of the hot fudge sauce over the ice cream sandwiches and spread it gently. Dollop half of the thawed whipped topping over the fudge and spread it around.

Layer the remaining 6 ice cream sandwiches over the first layer, then spoon on the remaining hot fudge sauce and finish with the remaining whipped topping.

Cover the slow cooker and set it on warm for 20 to 30 minutes, checking it at 20 minutes if your slow cooker runs warm. The sandwiches should be softened and the layers lightly melded, not fully melted or soupy.

Turn off the slow cooker once the dessert is soft.

Serve the dessert right away for a creamy, scoopable texture, or cover it and place the insert in the freezer for 1 to 2 hours for a firmer ice-cream-cake-like texture. If the insert is not freezer-safe, transfer the dessert to another freezer-safe container first.

Scoop the dessert into bowls and serve while cold. Strawberries or raspberries are optional accompaniments.