Using a vegetable peeler, remove 2 strips of lemon zest from the lemon, then squeeze out 2 tbsp. juice. In a small saucepan, combine the lemon strips, jam and 1/4 cup water over medium heat, stirring occasionally, until the jam melts. Remove from the heat and stir in the liqueur. Set the syrup aside.
In a large bowl, toss the berries, lemon juice and 2 tbsp. sugar. Let stand, tossing once.
Using an electric mixer, mix together the mascarpone and remaining 1/4 cup sugar at low speed until creamy, about 1 minute. Increase the speed to medium and gradually beat in the cream and vanilla. Continue mixing, increasing the speed a little at a time until you reach high speed and beating until the mixture is just thick and billowy. Do not overbeat.
Using a serrated knife, cut the cake cups in half crosswise (they should look like half-moons). Arrange one-third of the cake pieces in the bottom of a 12-cup trifle dish (or clear dish with straight sides), fitting them together in an even layer. Remove the lemon strips from the raspberry syrup and discard. Drizzle one-third of the syrup over the cake, then evenly cover with one-third of the berries. Top with one-third of the cream mixture, spreading with the back of a spoon until it reaches the edge of the dish. Sprinkle with 1/4 cup white chocolate.
Repeat the layering 2 more times. For the top layer, dollop the cream in a smaller mound on top of the berries, allowing some berries to show around the edge of the bowl. Cover the trifle dish with plastic wrap and refrigerate for at least 4 hours or up to 36 hours.