Preheat the oven to 170C/325F/gas 3.
Grease and line the cake tin with baking paper.
Grind the poppy seeds in the blender and whizz until all the poppy seeds have been broken up. You will end up with a black, fairly sticky, crumbly concoction.
Tip the poppy seed mixture into a bowl.
Separate the yolks and whites of the eggs into separate bowls.
Beat the yolks until thick then continue beating as you add the honey to the mixture a little at a time.
Stir in the blackberries and the poppy seed flour.
Beat the egg whites until they form into stiff peaks and gently fold them into the fruit and poppy seed mixture using a metal spoon.
Gently pour the batter into the cake tin.
Bake in the pre-heated oven for about 50 minutes or until a skewer poked into the centre of the cake comes out clean.
Allow to cool in the tin before turning out onto a wire rack.
