Prepare the Crumble: In a mixer with the paddle attachment, combine the crumble ingredients: all-purpose flour, sugar, almond flour, cold cubed butter, and crumbled amaretti biscuits. Mix at medium speed until the mixture is compact and crumbly. Set aside.
Make the Plumcake Batter: Using electric beaters or a stand mixer, beat the butter and sugar until light and fluffy. Add the peanut butter and continue mixing. Then add the eggs one at a time, mixing well after each addition. Sift together the flour and baking powder, then add to the mixture and mix thoroughly. Finally, fold in the heavy cream until fully incorporated.
Assemble the Cake: Butter and flour a plumcake mold with an insert. Pour the batter into the mold and level the surface with a spoon. Evenly crumble the prepared crumble mixture over the top.
Bake: Bake in a static (conventional) oven preheated to 180°C (356°F) for about 60 minutes. Check doneness with a toothpick before removing from the oven.
Prepare the Strawberry Jam Filling: Slice the strawberries and cook them in a saucepan over medium heat with water and sugar until soft and reduced. Blend the mixture until smooth. Add the softened gelatin sheets and stir well. Allow to cool, then transfer to a piping bag.
Cool and Fill the Cake: After baking, rotate the insert 360° inside the mold to detach the cake from the sides but keep it in place until the cake cools. Once cooled, remove the cake from the mold, fill the center with the strawberry jam using the piping bag, and decorate the top with fresh strawberries.
Chill and Serve: Refrigerate the filled and decorated plumcake until ready to serve.