Heat oven to 180C/160C fan/gas 4
and line a 20 x 30cm brownie tin with
baking parchment. Tip the butter and
chocolate into a non-stick saucepan and
melt over a low heat, stirring every now
and then, until smooth – take care not to
overheat it. Leave to cool.
Meanwhile, mix the sugar, flour, cocoa
and almonds with the xanthan gum. Stir
into the chocolate mixture, then beat in
the eggs and add the walnuts. Turn the
mixture into the tin, level with a spatula
and bake for 30-35 mins until firm and
just cooked – when tested with a skewer,
the crumb should still be a little moist.
Cool in the tin.
To make the icing, melt the butter in a
non-stick pan. Stir in the cocoa and cook,
stirring, for about 1 min. Add the icing
sugar and milk, and beat well. Pour on
top of the cooled cake, scatter with the
walnuts and lightly press them in. Leave
until set, then carefully remove from the
tin, strip off the baking parchment and
cut into squares. Will keep for several
days in a tin.