Heat oven to 180C/160C fan/gas 4
and line a 24 x 20cm brownie tin with
baking parchment. Put the butter,
dark chocolate and orange zest in a
non-stick saucepan and very gently melt
over a low heat, stirring every now and
then, until smooth – take care not to
overheat it. Cool.
Whisk the eggs and sugar together with
an electric whisk until the mixture is pale,
has doubled in volume and leaves a trail
when the beaters are lifted. Gently stir
into the cooled chocolate mixture. Sift
over the flour and cocoa, stir in, then
add the orange chocolate.
Pour into the lined tin and bake
for 35-40 mins. Cool in the tin, then
cut into squares.