Preheat the oven to 180°C/160°C fan/gas 4. You will need 2 x 8 inch cake tins greased and base-lined with baking parchment.
Heat up a pan of water until it is barely simmering.
Cut the butter into cubes and break the chocolate up into pieces then put in to a large heatproof mixing bowl. Place the bowl over the pan of water and allow the butter and chocolate to melt, stirring occasionally. Once melted, remove from the heat and put to one side for a couple of minutes to cool.
Once cooled, add the eggs and sugar and beat with an electric mixer until the batter is smooth; this should take a minute or so. Add the flour and fold into the mix with the raspberries.
Gently pour into the prepared tins, dividing the mixture equally.
Bake for 20-25 minutes. Once the cake starts to go golden brown and a skewer inserted into the middle of the cake comes out clean remove from the oven and leave to cool.