First whisk the egg whites until they have reached soft peaks. Scrape the egg whites out of the mixer or the bowl and set aside.
Don’t worry about cleaning the mixing bowl and into it add the butter, sugar and lemon zest then beat until light and creamy.
Add the egg yolks one at time.
Whisk together the flour and almonds then beat into the mixture as well.
Stir in the milk and lemon juice, the batter may look a little curdled but don’t worry about it.
Then fold in the egg whites into the lemon batter until completely incorporated and finally stir in the blackberries.
Pour the batter into a 1 litre ovenproof pudding dish and bake for 50 minutes. Check after about 35-40 minutes to make sure the surface isn’t browning too much, if it is place a tent of foil over the top.
Remove from the oven, leave for 10-15 minutes to rest then sprinkle with caster sugar and serve with whipped double cream.