Place the berries into a large bowl and sprinkle with half of the lemon juice. Lightly toss.
Combine the berries, sugar, cornstarch and remaining lemon juice in a saucepan over medium-high heat. Bring to a simmer and cook just until the berries begin to break down and give up their juices, about 3 minutes. Take the berries off the heat and let cool; the mixture should thicken up as is cools.
In a clean bowl, whip the cream with the sugar and the vanilla to soft peaks. Put the lemon curd into a second bowl and stir in a little of the whipped cream to loosen it. Then fold in the rest of the cream.
To assemble the trifle, spoon a layer of the lemon cream into a large glass bowl. Add a layer of pound cake, breaking the slices into pieces that fit. Then soak the cake with a layer of berries and their juices. Keep going to make 3 or 4 more layers, depending on the size of the bowl, finishing with a layer of lemon cream. Cover and refrigerate until ready to serve.