Prepare the blackberries. Thoroughly wash the blackberries, discarding any spoilt fruit. Place onto a double layer of kitchen roll to gently dry them.
Preheat the oven to 180℃ / Fan 160℃ / 355℉ / Gas 4. Grease and fully line a 15cm (6in) cake tin with baking parchment.
Beat the butter and sugar until very pale and fluffy. Beat in the almond extract. Then gradually add the beaten eggs a little at a time, beating well after each addition.
Sieve the flour, ground almonds and baking powder into the mixture. Use a spatula or large metal spoon, fold in gently. Add a little milk and gently mix in until the batter has a nice dropping consistency.
Place the prepared blackberries into the bottom of the cake tin, squashing them in as necessary to ensure the whole surface is covered. Spoon the prepared batter onto the blackberries. Spread level, then make a slight indentation to the centre of the batter.
Bake the cake tin in the centre of the oven for about 45 - 50 minutes until golden brown, slightly pulling away from the sides and a cake skewer inserted in the centre comes out clean.
Once baked, remove from the oven and place onto a cooling rack. Allow the cake to cool for 5 minutes before turning out onto a serving plate. Carefully remove the baking parchment.
Serve warm or cold on its own or with some ice cream, cream or yogurt.