Heat oven to 180C/fan 160C/gas 6 and line
the base of a 20cm square shallow baking
tin with baking parchment. Melt 100g dark
chocolate, all of the milk chocolate and the
butter in a heatproof bowl over a pan of
simmering water. Remove from the heat,
then stir in the sugars. Cool a little while you
prepare the rest of the ingredients.
Stir the eggs into the chocolate mixture,
followed by the flour, walnuts and a pinch
of salt until really well combined. Pour the
mixture into the prepared tin, then bake for
25-30 mins until an inserted skewer comes
out with sticky crumbs. Cool in the tin.
For the dip, gently melt the remaining
chocolate as above, then stir into the yogurt
and chill. To serve, cut the brownies into
chunks, then spoon the dip into small bowls.