1. Combine the strawberries, blueberries, raspberries, and blackberries with the sugar in a large bowl and let stand 30 minutes.
2. Stir the jam and lemon juice together in a small bowl and set aside.
3. Combine the heavy cream and confectioners’ sugar in a cold bowl and beat with an electric mixer to stiff peaks.
4. To assemble the trifle, form a layer of the pound cake on the bottom of the trifle bowl. (Cut slices of cake into strips to make them fit in a single even layer). Brush the cake lightly with some of the jam mixture. Spoon one-third of the berries on the cake; top with about a third of the whipped cream. Repeat the layers two more times with the remaining pound cake and fruit. For the final whipped cream layer, spoon a decorative mound in 4-inch diameter in the center.

For the Lemon Pound Cake: 

1. Preheat the oven to 325°F. Butter and flour a 9-inch by 5-inch loaf pan.
2. Combine the butter and sugar in the bowl of an electric mixer and beat on high until light and fluffy, about 2-3 minutes. With the mixer on medium, beat in the eggs 1 at a time, stopping to scrape down the sides of the bowl after each. Beat in the sour cream, lemon juice, lemon zest, and extract until well combined. In a separate bowl, combine the flour, baking powder, and baking soda. With the mixer off, add the flour mixture to the butter mixture. Beat on low until well combined, about 45 seconds. Pour batter into the prepared pan.
3. Bake in the center of the oven until the top is browned and cracked and a toothpick inserted into the center comes out clean, 60-65 minutes. Let cool completely in the pan on a wire rack.