(click on the text to highlight each stage):
- Whisk the eggs and sugar until combined. Melt the chocolate and butter in a bowl over a pan of simmering (not boiling) water or in a microwave oven. Stir in the yoghurt. Gently stir into the egg mixture.
- Sift the dry ingredients together and gently fold into the chocolate mixture until well combined. Pour the mixture into a 23cm/9 inch greased square tin and bake for about 45 minutes Gas mark 4/180ºC/350ºF until cooked through.
- Leave in the tin for 15 minutes, and then turn out onto a wire rack to become cold. Store in an airtight tin.