Sieve the flour, cocoa and baking powder to get an airy brownie.
Melt the butter and chocolate au bain-Marie. Do this by hanging a heatproof bowl above a pan with boiling water (the bowl can't touch the water). The bowl will get warm and therefore the chocolate and butter will melt. This method is used when you want to warm ingredients slowly and you don't want to burn them.
Because this is a brownie it might be slightly wet on the inside. It's supposed to be. Check if it's done with a skewer won't work.
Line a springform with baking paper.
Preheat the oven to 350 degrees Fahrenheit (175 degrees Celsius).
Put a pan on the stove with some water and hang a heatproof bowl above the water. Bring the water to the boil
Put the chocolate and butter in the bowl and let it melt.
In the meanwhile beat the eggs with the sugar in a second bowl for 5 minutes.
Sieve the flour, cocoa, salt, and baking powder above the eggs and mix them gently with a spatula.
Then pour the chocolate mixture with the batter and mix them gently with the spatula through.
Pour the batter into the springform.
Flatten the top of the cake.
Spread the raspberries on top.
Bake the cake in the oven for 35 minutes.
Let it cool down on a rack when you have taken it out.