Preheat the oven to 200˚C/180˚C fan/gas mark 6. Grease and line a 30 x 20cm rectangular baking tray. Unroll the pastry and carefully transfer to the prepared tin, pressing it gently into the corners and trim away any excess.
Cover the top of the pastry with a sheet of baking parchment and fill with a layer of baking beans or raw rice. Bake for 15 minutes until lightly golden. Carefully remove the baking beans or rice and baking parchment. Spread the pastry with jam and set aside.
Lower the oven temperature to 190˚C/170˚C fan/gas mark 5. Put the butter in a mixing bowl with the caster sugar. Whisk together until creamy and light in texture and colour.
Gradually beat in the eggs and Almond Extract until combined. Add the ground almonds and sift the flour and Baking Powder on top. Using a large metal spoon, carefully fold into the mixture.
Finally add the raspberries and very gently stir through the mixture being careful not to break up the raspberries.
Spoon the mixture over the jam and smooth over the top. Bake for 35-40 minutes until risen, golden brown and just firm to the touch. Leave to cool completely in the tin before carefully removing and placing on a board.
Sift the icing sugar into a bowl, add approx. 45ml (3 tbsp) of warm water and mix to make a fairly thick icing. Pour the icing over the top of the bakewell and spread to generously cover, letting it drip down the sides.
Sprinkle the flaked almonds and raspberries over the top of the icing. Leave the set for a few minutes and your bakewell is ready to slice up and enjoy!