Rinse the chaga mushroom chunks quickly under cool water to remove any debris.
If using chunks, break them into smaller pieces to help release flavor.
Add the chaga and filtered water to a saucepan.
Bring to a gentle simmer over low to medium-low heat. Avoid boiling.
Let simmer uncovered for 45–60 minutes, until the liquid turns deep amber or dark brown.
Remove from heat and strain the tea into mugs or a teapot.
Add optional spices or sweeteners to taste and serve warm.
Save the used chaga—re-brew it 2–3 more times until the color fades.