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Heat the oven to 160°C (140° fan) 325°F gas 3. Line a large baking tray with non-stick baking paper.
Whisk the egg whites and salt in a mixing bowl until stiff.
Gradually whisk in the sugar and vanilla until evenly combined.
Sift in the cocoa, cinnamon and flour and whisk until blended.
Put the mixutre into a piping bag and carefully pipe the alphabet or other shapes onto the tray, leaving enough space for the biscuits to spread.
Bake for 12-17 minutes until golden brown. The biscuits will be a little soft, but will crisp as they cool. Cool on the baking tray for a few minutes, then place on a wire rack to cool completely.