Heat the oven to 180C/350F. Line a 20 x 30cm baking tray tin with baking parchment.
Put the chocolate, butter, and sugar in a pan and gently melt, stirring occasionally with a wooden spoon. (you may also melt the butter and chocolate in the microwave for about 1-2 minutes, making sure you take out the mixture and give it a stir every 30 sec. This will help not burning the chocolate)
Place the melted chocolate mixture into a large bowl. Add in the eggs, vanilla essence and brown sugar.
Sieve over the flour and whisk for about a minute or so, until you have a smooth batter.
Fold in the raspberries, then pour the mixture into your baking tray. Spread it evenly with a spatula.
Bake on the middle shelf for 50 mins or, if you prefer a firmer texture, for 10 mins more. Cool before slicing into squares.
Keep it in the fridge, stored in an airtight container for up to 3 days.