Step 1: In a medium bowl, combine 3 cups of the hybrid berries with the granulated sugar and lemon juice. Mash about 1/4 of the berries with a fork to release their juices. Let sit for 20 minutes to macerate.
Step 2: In a large mixing bowl, beat the heavy cream, mascarpone cheese, powdered sugar, and vanilla bean paste until medium-stiff peaks form. Do not overbeat.
Step 3: Arrange half of the pound cake cubes in the bottom of a large glass trifle bowl or individual jars.
Step 4: If using, drizzle the berry liqueur evenly over the cake layer.
Step 5: Spoon half of the macerated berry mixture (including the syrup) over the cake.
Step 6: Spread half of the mascarpone cream mixture over the berries, smoothing it to the edges of the bowl to create a distinct layer.
Step 7: Repeat the layers with the remaining cake, berries, and cream.
Step 8: Garnish the top of the Blackberry Hybrid Fruit Trifle with the remaining 1 cup of fresh whole berries.
Step 9: Cover and refrigerate for at least 4 hours, or overnight, before serving to allow the flavors to meld.