Line the baking dish or brownie pan with baking paper.
Break the chocolate up into pieces and place in a microwaveable bowl. Microwave on medium power. Check after 60 secs, stir and continue if not melted at all.
Add butter and repeat for another 60 secs. Stir until it's all melted and combined. Leave it to cool for a few minutes.
Beat the eggs, add sugar gradually and continue till mixed well. Add the vanilla.
Add the chocolate mix into the egg and sugar mix, continue beating slowly for half a minute.
Add the flour and combine everything. I use a tabletop mixer and just do it all in it.
Pour into the dish/tin and bake for about 45 minutes.
Cool and cut into squares., sprinkle icing sugar just before serving.
Notes
I have a huge tray bake tin (13 x 10) that I sometimes use when I need lots of brownies, same recipe, just double all the ingredients and bake for about 60 minutes or so.