Step 1

Line a dish or tin roughly 18×35cm or 25cm square, with baking parchment (not greaseproof paper). Heat 300g of the raspberries in a microwave on high until piping hot and breaking down, then mash in a sieve with a fork to extract as much juice as you can – you should get nearly 200ml.

Step 2

Put the gelatine leaves in a large bowl of cold water one by one to soften.

Step 3

Put the sugar, liquid glucose and 200ml water in a narrow, deep, saucepan. Heat gently until the sugar dissolves, then boil. When the sugar is nearing 125C on a sugar thermometer, whisk the egg whites to stiff peaks in a large bowl, with another bowl close. When the syrup reaches 125C, pour, in a steady stream, into the egg whites (not the whisk blades) while you continue whisking.

Step 4

Squeeze any excess water from the individual gelatine leaves and beat these in too – the heat from the sugar syrup will dissolve them. Once all leaves are in and no gelatine streaks are visible, add the raspberry juice and continue whisking for about 10 mins until the mixture is very thick.

Step 5

Working quickly, transfer roughly half the mixture to the second bowl. Whisk enough food colouring into one of the bowls to get a rich raspberry colour. Gently stir in the remaining raspberries. Alternate dollops of the mallow mixtures into the lined dish and use the end of your spoon or spatula to swirl together. Leave to set (not in the fridge) for a few hours until firm.

Step 6

Sift together the dusting ingredients (with raspberry powder if you want), then turn the marshmallows out onto a board, peel off the lining paper and cut into chunks. Toss with the dusting sugar to lightly coat. Store between sheets of parchment in an airtight tin and eat within 3 days.