Place the prunes in a bowl. Mix the jasmine tea with 1 tablespoon yuzu juice and pour over the prunes. Add the orange and lemon peel, stir to mix, then cover and leave overnight.
Grease a 2lb (1kg) loaf tin and line it with baking parchment. Leave a reasonable amount of parchment poking out round the edges.
Preheat the oven to 150 C / Gas 2.
Drain the prunes, keeping the soaking liquid and discarding the orange and lemon peel. Squash the prunes a bit to make sure they aren't too soggy. Chop them up into smallish pieces.
Sieve the gluten free flour, baking powder and psyllium husk powder together in a bowl.
In another bowl cream the butter and sugar together until well combined. Add the beaten egg and combine well.
Slowly add the flour mix and mix well. It'll be quite stiff at this stage so it is best to use an electric mixer.
Mix the matcha tea powder with the hot water and whisk well to combine. Pour the tea into a strong glass and place it into some iced water to cool it quickly. If the water is too hot or you leave it to brew for too long the tea will become bitter.
Pour the cooled matcha tea into the cake mix and whisk well until you have a smooth, bright green batter.
Fold the chopped soaked prunes and white chocolate chips into the batter with a spatula.
Dollop the mix into the prepared loaf tin and smooth it out with a spatula or the back of a spoon.
Bake until a skewer inserted in the middle comes out clean, about 1 hour. The baking time will vary a bit depending on the exact flour you used and how soggy the fruit was.
Just before the cake is due out of the oven, take the reserved soaking liquid and place in a small saucepan over a medium heat. Add 30g sugar and 1/2 tablespoon yuzu juice and reduce until you have a light syrup (if you reduce it for too long it will turn into toffee).
Remove the cake from the oven, keep in the tin and use a skewer to poke a fair few holes in it. Now pour the hot syrup over the top.
Leave to cool in the tin for 5 to 10 minutes, then take it out and place on a wire rack to finish cooling. Best served on the day, preferably when still slightly warm although it will last a couple of days in an airtight container.
Use prunes that are really dry and not semi-dry and soft.