1) Preheat the oven to gas mark 4, electric 175°C or 350°F. Line a baking tin with greaseproof paper
2) Place the chocolate drops and butter into a bowl and place over a pan of hot water, making sure that the base of the bowl isn’t touching the water and being careful not to get any water in the bowl with the chocolate in. Leave to melt gently, stirring occasionally, then remove from the heat.
3) In a second bowl add the sieved flour to the cocoa powder, baking powder and the salt.
4) In a third bowl beat the eggs and sugar together until combined. Add the vanilla. Then fold in the melted chocolate.
5) Fold in the flour mixture making sure it is all well mixed together. Spoon into the baking tin and bake for 25 minutes. Allow to cool before cutting.