This is a simple recipe for a matcha mousse cake that can be made with just four ingredients and is free of eggs, butter, and milk. A tart base is made by mixing crushed cookies and matcha powder, and then a mousse batter made by mixing white chocolate, matcha powder, and whipped cream is layered on top and chilled until firm. The result is a fluffy and smooth mousse cake with a perfect balance of matcha aroma and white chocolate sweetness, and it's ready to make just by mixing and chilling. Tips for mixing the matcha to prevent lumps and for gently mixing the whipped cream and batter are also included.