In a bowl, mix the icing sugar
with the cornflour and set aside.
Dissolve the gelatine in 150ml
hot water in a heatproof jug. Line
a 20cm x 30cm tin with baking
parchment and dust with some
of the icing sugar mix. Put the
granulated sugar and liquid glucose
in a heavy-bottomed pan with
200ml water. Cook over a low heat
until the sugar has dissolved
completely, turn up the heat and
boil until the mixture reaches firm
ball stage on a sugar thermometer
(125C/256F) – around 10-15 mins.
If you don’t have a thermometer,
drop a little of the mix into a glass
of very cold water – if it sets into
a squidgy ball, it’s ready. While the
sugar is boiling, use an electric
whisk to beat the egg whites until
stiff. When the syrup reaches the
right stage, pour it into the jug with
the gelatine water; be careful as it
will be very hot and may bubble up.
Continue whisking the egg
whites while pouring on the syrup
in a steady stream, then adding
the vanilla extract – the mixture
will go shiny and start to thicken.
Continue whisking for about
10 mins until very stiff. Pour half
the egg white mixture into the tin,
then scatter over the berries. Top
with the remaining mixture and
leave somewhere cool and dry
to set for at least 2 hrs until firm.
Lay a large sheet of baking
parchment on a chopping board
and sprinkle on the remaining icing
sugar mix. Turn the marshmallows
out and cut into squares, rolling them
in the sugar mix. Keep in an airtight
container but best eaten on the day.