Elderflower White Chocolate Mousse Cake with Rhubarb Filling

"After several sweet requests, I have made a new version of my elderflower white chocolate mousse cake using elderflower cordial instead of fresh elderflowers to make it possible to make all year around. I also added raspberries to the rhubarb filling. All the sweet cherries pictured are from my father-in-law’s summerhouse garden. What a Sunday treat!"