Step 1

Preheat the oven to 180°C/160°C fan/350°F/gas mark Grease a 20cm/8inch square metal cake tin and line with baking parchment.

Step 2

Sift together the flour, cocoa powder, baking powder, espresso powder and salt and set aside.

Step 3

Place the milk, yogurt and sugar in a medium sized pan over a low heat. Stir often until the sugar has dissolved and the mixture is hot and glossy looking but not yet simmering.

Step 4

Remove from the heat and add the chopped chocolate and cocoa butter and the vanilla extract. Stir until melted and smooth.

Step 5

Tip in the dry ingredients and stir until no dry lumps remain. The batter will be quite thick. If you wish to add any mix-ins such as chocolate chips or chopped nuts then mix them in now.

Step 6

Transfer the batter to the prepared tin and spread it level. Smooth the top with a spatula or the back of a spoon.

Step 7

Bake for 20-30 minutes, until a skewer inserted into the centre comes out gunky with moist crumbs but no wet batter. If it comes out clean that means they are over-baked so keep an eye on them.

Step 8

Leave the brownies to cool completely in the tin before slicing into squares. Store in an airtight container for up to a week.