Lightly toast the fennel seeds, cardamom, cloves, cinnamon, peppercorns, and bay leaf in a small dry pan over medium-high heat just until fragrant, about 1 minute.
Crush the spices a bit in a spice mill or with a mortar and pestle, then transfer to a stainless steel saucepan. Add the ginger and pour in the milk. Bring to a gentle simmer and cook for 2 minutes. Add the tea leaves, turn off the heat, cover the pot, and let steep for at least 5 minutes.
Strain the chai into warmed cups and sweeten to taste.