Preheat the oven to 180 celsius degrees or 350 fahrenheit degrees
Spray a large baking tray with non-stick spray (or grease with butter if you prefer)
Line it with parchement paper leaving some edges hanging on outside, then spray or grease the parchement paper too
Mix together the flour, salt and baking powder in a bowl
In another large bowl put the butter and the chocolate and heat them in the microwave until the butter is melted, about 90 seconds; this can be also achieved over a pot with simmering water
Whisk the butter – chocolate mixture until the chocolate is melted and the mixture is smooth
Pour the sugars into the mixture and whisk well
Add the eggs, the egg yolk and vanilla and continue stirring
Fold in the flour mixture and incorporate it well
Finally, add the chocolate chips
Pour the batter in the prepared baking tray and bake the brownie 20-25 minutes or until the skewer comes out clean from the middle of the cake
Take the brownie out of the oven and let it cool down before adding the glaze
Take the fudge brownie out of the baking tray by the parchement paper edges and put it on your working surface
Preparing the glaze
Combine the cocoa, powdered sugar and vanilla in a small bowl
Add half of the hot water and whisk well
Keep adding small amounts of water until the glaze can be just poured over the fudge brownie
Pour the glaze over the fudge brownie and level it with a spoon or a spatula
Let the glaze chill down for 30 minutes or more, then cut small, rectangular fudge brownies and pile them on a nice plate