Simmer the tea, honey, juniper berries, star anise and white peppercorns for 10 minutes.
Remove and strain through a cloth or fine sieve.
Add 60 ml lemon juice and the grated rind of 1 lemon and place in the freezer. When the icicles start to form, loosen the mixture with a fork. Place back in the freezer and loosen again after 2 hours. Freeze once more, loosening again before use.
Add a tot of gin to each glass.
Spoon the granita to fill the whole glass and add the tonic water. Garnish with a slice of orange or lemon.
Notes
Keep granita in a sealed container in the freezer.