Preheat the oven to 180 C (350 F) and grease and line a deep 9"x13" tray with baking paper.
Combine the flour, baking powder and salt in a medium bowl and set aside.
In a stand mixer fitted with paddle attachment, beat the butter and sugar until very light and fluffy.
Add the eggs, one at a time, beating well between each addition. Beat in the vanilla.
On a low speed, mix in a third of the dry ingredients until just combined, then follow with half the buttermilk. Continue alternating the wet and dry ingredients until they are just combined, finishing with dry. Fold in the berries.
Transfer the batter to the prepared tin and spread out evenly. Bake for 30 - 35 minutes until the cake is lightly golden and springs back when pressed in the centre. Set aside to cool.
FOR THE PANNA COTTA
When the cake has cooled down a little, but not completely, make the panna cotta.
Bloom the gelatin by placing the sheets into a bowl of cold water and allowing to stand.
In a small saucepan, heat the cream, sugar and vanilla, just until bubbles begin to appear around the edges.
Remove the cream from the heat. Squeeze the water out of the gelatin sheets and stir them into the cream mixture.
Pour the hot panna cotta straight over the sponge. Allow to sit at room temperature for an hour, before transferring to the fridge to set overnight.
GANACHE AND ASSEMBLY
To make the ganache, heat the cream, chocolate and milk in a small saucepan over a low heat until melted, smooth and combined. Set aside.
Cut the lamingtons into 20 even squares.
Dip each lamington into the ganache, then roll in shredded coconut and place on a lined baking tray. Return the lamingtons to the fridge for half an hour to set the ganache.
Keep the lamingtons refrigerated, but allow to come to room temperature to enjoy at their best, softest texture. Makes 20.
Happy baking!
Recipe by Butter Baking at https://www.butterbaking.com/2016/05/30/panna-cotta-lamingtons/