Preheat your oven to 180C/350F/Gas mark 4. Lightly grease or line an 8x10 inch tin with baking parchment.
In a food processor, blitz the beans along with the melted butter, sweetener and agave syrup. Don't worry if you can't make it 100% smooth. Just make it as smooth as you can.
Transfer the bean mix to a large mixing bowl.
Stir in the eggs and egg whites.
Mix in the almond extract.
Fold in the flour, ground almonds and baking powder.
Then gently fold in 2/3rds of the blueberries. Pour the batter into your prepared tin.
Sprinkle the remaining blueberries and almond flakes over the top of the batter and gently press on them so they stick to the cake batter.
Place the cake into your hot oven and bake for 45 minutes.
Test the cake with a skewer, if it comes out clean then your cake is baked through. If not then give it a couple more minutes. And test again.
Leave the cake to cool in the tin for 10 minutes, then transfer to a wire rack to fully cool down.
Slice your cake into 12 squares and enjoy.
Keep the cake in an airtight tin for up to 7 days. This cake can also be frozen for 2 months. Defrost overnight in the fridge.