Chop the white chocolate and place it in a bowl.
In a small saucepan, heat the heavy cream together with the forest berry puree until just simmering (do not boil too much).
Pour the hot mixture over the white chocolate. Let sit for 1 minute.
Stir until smooth and fully combined.
Add the butter and mix until glossy and silky.
Cover with plastic wrap touching the surface and refrigerate for 4–6 hours or overnight until thick enough to pipe.
Before using, let the ganache sit at room temperature for 10–15 minutes, then transfer to a piping bag and fill macarons.
