Spray a 9-by-13-inch baking dish with nonstick cooking spray. Place a cooling rack on a baking sheet.
Heat a large saucepan or Dutch oven over low heat, then add the butter and heat until melted. Add the marshmallows and stir until just melted, then stir in the cereal, salt and 1 cup raspberries until the cereal is coated. Use the cooking spray to spray your hands or a spatula and press the marshmallow mixture into the baking dish in an even layer.
Let set up, 15 to 20 minutes, then add the cream and chocolate to a small saucepan. Stir over low heat until the chocolate is completely melted and combined. Remove to a bowl.
Cut the treats into 1-inch squares and place on the cooling rack. Dip one corner of each treat into the chocolate, then return to the cooling rack and sprinkle with a little of the remaining raspberries. Let the chocolate cool completely, then serve.