Step 1- Build the Raspberry Layer
In a food processor, blend the raspberries with half the lemon zest and juice until smooth. Add 1 3/4 cups of the softened vanilla ice cream and pulse until combined. Spread this mixture evenly in the parchment-lined loaf pan and smooth the top with a spatula, then spread half the raspberry preserves over the layer. Freeze for 1 hour until set.
Step 2- Add the Vanilla Layer
Spread 3/4 cup of softened vanilla ice cream over the raspberry layer. Smooth the surface, then spread the remaining raspberry preserves on top. Freeze for another 1 hour until set.
Step 3- Build the Blueberry Layer
Blend the blueberries with the remaining lemon zest and juice in the food processor until smooth. Add the remaining 1 3/4 cups of softened vanilla ice cream and pulse until combined. Spread this mixture evenly over the vanilla layer and smooth the top, then freeze for at least 2 hours until fully set.
Step 4- Unmold and Serve
Remove the cake from the loaf pan by lifting the parchment paper. If it sticks, run warm water over the outside of the pan to loosen it. Slice with a sharp knife and top with fresh berries before serving immediately.