Preheat oven to 175C/350F. Line and grease a 32cm X 27cm baking tray a similar size would work but you need to make sure you can but it into 3 pieces the length and width of your bread/meatloaf/rectangular tin (mine was 10cm x 24cm).
Place the egg whites into the clean bowl of a kitchen stand mixer fitted with a whisk attachment.
Whisk the egg whites on medium/high until soft peaks form.
Slowly add the maple syrup, 1 tablespoon at a time, until large peaks have formed,
Continue whisking on medium/high and add the vanilla extract.
Add the egg yolks, one at a time. Only add the next yolk when the previous one has been fully incorporated. Whilst still whisking, add the milk and vinegar into the egg mixture.
In a separate bowl, lightly whisk the coconut flour and baking powder together. Ensure that the coconut flour has no lumps in it.
Turn the whisk to low and add the flour mixture. (If you keep it on high then you will most likely end up wearing the flour). Once incorporated, return the whisk speed to medium/high to fully mix all the ingredients.
Pour the batter into the tray and smooth out the top. Bake for 25 minutes or until a toothpick inserted in the centre comes out clean.
Once cooled, cut the cake into 3 equal pieces that will fit inside the rectangular tin which the Lamington Ice Cream Cake will be formed in.