Place the coffee beans and cardamom in a pestle and mortar and crush to a very coarse consistency – there should still be small chunks of coffee beans.
Place the crushed coffee mixture, cardamom and cold water in a large glass jar. Stir well to combine, seal and leave overnight to infuse, a minimum of 12 hours (24 hours is best).
Strain the mixture through a fine sieve or muslin. Fill 4-6 large wine glasses with ice then pour 60ml cold brew coffee over each. Divide the orange blossom water between the glasses, add an orange peel to each and top up with tonic water.
Stir to mix everything together. Hold a lighter to the remaining orange peel before squeezing, causing a burst of orange oil to flame. Run the orange peel across the rim of the glass, and serve immediately.
Make a big jug of the cold brew coffee mix or serve it in a punch bowl so guests can serve themselves.