In a small saucepan, add the water, sliced fresh ginger, cardamom pods, peppercorns, cloves, and cinnamon stick. Bring to a gentle boil, then reduce heat and simmer for 5 minutes to extract the flavors.
Add the loose black tea (or tea bags) to the saucepan. Simmer for 2 minutes more.
Pour in the oat milk and stir. Increase heat slightly until the mixture returns to a gentle simmer. Cook for 3–4 minutes, watching carefully so it does not boil over.
Add the sugar and stir until fully dissolved. Taste and adjust sweetness as desired.
Strain the chai into cups using a fine mesh sieve. Serve hot and enjoy the creamy, spicy aroma.
Notes
If you have any extra spiced chai or you want to make a big batch, you can refrigerate it for 2 to 3 days in an airtight container. Warm over low on the stovetop or in the microwave.