Grease and line an 8x8inch square tin and set aside. Then preheat the oven to 200C/180C Fan/Gas Mark 6.
Very finely chop the chocolate and place into a large bowl. Then melt the butter and pour over the chocolate, stirring until completely melted. Then mix in the sugar and stir to combine. Then the flours and salt, again stirring to combine. Finally add the yoghurt and stir to combine.
Pour the brownie batter into your prepared tin and level out.
Bake in the oven for 30-35 minutes. A skewer inserted should still have some brownie batter on when they're done. Then leave to cool completely in the tin before cutting into 8 slices.
Brownies can be kept for 4-5 days in an air-tight container.