Then mix them with the beaten sugar, add the yoghurt with baking soda and stir carefully until homogenized. Beating with a mixer is not recommended, it's best to use a spatula so that the yoghurt doesn't get too runny.
Pour the resulting thick mixture into a tray which you've laid out with baking paper. If it has a nonstick coating, then you can just smear it with butter.
If using a rectangular tray, use one measuring 6″ (15 cm) x 8″ (20 cm). If it's round, use one with a diameter of 10″ (26 cm).
Bake at 338°F (170 °C) for 40-45 min., then leave the brownie to cool.
Once it's cooled, cut it into rectangles or rhombuses and prepare the glaze. For it, mix the sugar, water and cocoa in a suitable container, leave to boil.
Add the chopped butter and stir until it melts and homogenizes. Pour the glaze over the cut brownies and leave to sit for at least 1/2 an hour prior to consumption.