To make the crumble, combine all the ingredients in a bowl and use your hands to fully rub in the butter. Spread on a tray lined with baking paper and bake in the oven at 170°C for 8–12 minutes,or until the mixture is looking golden. Set aside.
Generously grease the bowl of your slow cooker. Set the cooker to low to warm up while you prepare the pudding.
Cream the butter, 200 g (7 oz) of the sugar and the lemon zest in the bowl of a freestanding electric mixer fitted with the whisk attachment until creamy and pale. Add the eggs, one at a time, and beat until combined.
Gently stir through the flour and milk until just combined. Pour the batter into the bowl of your slow cooker. Combine the yuzu juice, lemon juice, boiling water and remaining sugar in a jug and gently pour over the batter.
Cover the slow cooker with a tea towel (dish towel) and close the lid. This will prevent any moisture from the cooker dripping onto the pudding. Cook for approximately 1 hour 40 minutes.
You want the top of the pudding to look cake-like and set, but not the bottom. If you are unsure, remove the bowl from the slow cooker and give it a gentle wiggle. The top should hold firm, but you will get some movement due to the liquid underneath.
Return to the cooker and continue to cook, checking every 10–15 minutes, until cooked to your liking (keep the cooker lid ajar for this last stage of cooking so you can check on it easily).
Given this is the style of pud you can’t remove from the cooker in one piece, I either take the entire bowl to the table or scoop onto individual plates. To serve, scatter over the baked crumble mixture and edible flowers, and garnish with lemon.