Method
Melt butter.
Add chocolate powder and whisk until melted and glossy.
In a separate bowl, beat together eggs and sugar.
Mix this into the chocolate.
Sieve in the plain flour and beat until smooth.
Pour mixture into a lined, 9 inch (23cm) square tin.
Bake at 180C for 20 minutes.
Cool in the tin for 10 minutes before cutting into squares.