In a large pot filled with 1.5 litres of water, add ginger, cinnamon, nutmeg pieces, cloves and cardamom pods. Bring to the boil, cover the pot with a lid and allow to simmer for 30-40 minutes until the water is fragrant.
Remove from heat and stir in sweetener. Cool the liquid down to room temperature or colder.
To serve, strain liquid through a sieve into glasses filled with ice. Top with a little milk and grated nutmeg.