Put most of the forest fruits (reserve a handful to decorate) in a food processor with the golden syrup and most of the icing sugar. Whiz together until smooth.
Put one half of a brownie on a plate and top with a spoonful of the berry purée, followed by a small scoop of ice cream. Top with the other brownie half. Repeat with the remaining 3 brownies.
Decorate each plate with a few reserved frozen berries and a spoonful of extra purée. Dust with a little icing sugar and serve.