Step 1

In a large mixing bowl, combine the strawberries and sugar. Let rest 10 minutes then lightly mash. (Alternatively, mash strawberries without sugar.) Fold in the Cool Whip; set aside.

Step 2

Remove cake from package and invert onto serving platter. Use a serrated knife to slice cake in three layers. Remove top two layers and spread a layer of strawberry mixture over bottom layer of cake. Top with middle cake layer and spread more mixture on second layer, then place remaining layer of cake on top.

Step 3

Fold marshmallows into remaining strawberry mixture in bowl. Evenly spread over outer edges of cake until fully covered.

Step 4

Refrigerate at least 2 hours before serving so the marshmallows have time to soak in the juices. Slice and serve.