Preheat the oven to 180C / 160C fan / 350F. Line a small springform pan (7 inches) with greaseproof paper on the base and generously butter the sides.
Separate the eggs and beat the egg whites until stiff.
In a clean bowl add the egg yolks and sweetener. Blend using an electric whisk for 2 minutes until pale + fluffy. Add the sour cream, melted and cooled butter, almond milk, vanilla and lemon zest. Whisk to combine.
In another clean bowl, mix the almond flour, coconut flour and baking powder together.
Add the dry ingredients to the wet and mix to combine with an electric whisk. Last, fold in the egg whites with a spatula until combined. Don't over-mix to keep the air bubbles intact.
Pour into your springform pan and level the top with a spatula.
Bake for 50 - 55 minutes or until you can insert and remove a skewer without it sticking. Loosely cover with a sheet of tin foil if it starts to brown a bit too much on top, from about 45 minutes. Let cool before releasing from the springform.
While the cake is baking, add the frozen raspberries, sweetener and water to a pan. Simmer for about 3 - 5 minutes until the raspberries are soft. Mash with the back of a spatula. Turn off the heat and add the chia. Allow to fully cool to firm up.
Whip the cream until just under stiff peaks.
Cut the fully cooled cake in half lengthways using a sharp knife. Add a layer of raspberry jam and cream and top with raspberries. Add the top of the cake and dust with powdered sweetener. Slice and serve.