Line a 25cm/8" square baking tin with greaseproof paper. Or if your tin is silicone, you don't need to do this step
In a large bowl over some simmering water, melt the chocolate and stir until smooth.
If you are using butter rather than oil, add it into the melted chocolate and stir until the butter is also melted
Beat the eggs and whisk into the melted chocolate until you have a smooth consistency. It will probably thicken a little.
In a separate bowl, mix together the flour, sugar and oil (if using), then add this to the chocolate mixture. Stir together well.
Pour your brownie mix into the baking tray, and bake for around 25 minutes. If your baking tray is silicone, you may need to stand it on a baking tray as well
Click here to start a 25 minute timer
You don't want to overcook them so, they should be slightly springy on the outside but still gooey in the middle. Allow to cool in the tray, then cut into 20 squares.