Remove cake from foil pan and line pan with a long piece of plastic wrap allowing for overhang.
Cut lumpy mound off top of cake. Melt butter in a saute pan and crumble top of cake into pan. Saute until crumbs are browned, then set aside to cool.
Slice cake horizontally into 3 even slices.
In a medium bowl, mix together berries, jam, lemon zest, and lemon juice. Set aside.
In chilled bowl, beat on high speed heavy whipping cream, powdered sugar, and vanilla until stiff peaks form.
Place one layer of cake on bottom of foil pan. Evenly spread 1/3 of berry mixture, then evenly spread 1/3 of whipped cream.
Repeat layers 2 more times: cake, berry mixture, and whipped cream. Lightly cover top of dessert with plastic wrap and refrigerate for 8 hours, or overnight.
Before serving, lift cake from foil pan using plastic wrap overhang, and set on plate. Sprinkle with optional buttery crumbs, more berries, and a spring of fresh mint. Enjoy!
Notes
Frozen whipped topping can be substituted for the homemade whipped cream.