Preheat oven to 160c. Grease and line a 20 cm x 30 cm shallow baking tin.
Melt butter and chocolate in a saucepan over low heat until melted and combined. Cool slightly.
Sift flour and cocoa together then stir in brown sugar, chocolate drink powder and pecans.
Add eggs to chocolate mixture and stir until smooth. Pour into flour mixture and mix until combined. Spoon into prepared tin and bake for 50 – 60 minutes. Cool in the tin then cut into squares.