In a large bowl, add cold heavy cream, confectioner's sugar, and vanilla extract. Whip with a hand mixer or stand mixer until medium peaks have formed. Add strawberry jam and gently fold into whipped cream until evenly incorporated. Set aside.
In an 8x8 square pan, add a thin layer of whipped cream (this layer is not repeated). Top with a single layer of graham crackers. Top graham crackers with a thick layer of whipped cream, spread into an even layer. Top whipped cream with a single layer of strawberry slices. Repeat these layers two more times, for 3 layers each of graham crackers, whipped cream, and strawberries.
Cover and refrigerate for 1 hour for a firm cake, or 3 hours for a softer cake. Graham crackers will continue to soften over time and cake is best served within 24 hours.
Slice and serve cold.
Heavy cream, confectioner's sugar, and vanilla extract can be substituted with 4 cups of Cool Whip.
Amount of graham crackers may vary based on size of pan used. Graham crackers can be substituted with vanilla or chocolate wafers.
Whipped cream can only be made with heavy cream or heavy whipping cream - light cream, half & half, or whole milk cannot be substituted.