Combine the mauby bark, 4 cups water, cinnamon, cloves, orange peel, and star anise in a saucepan. Bring to a boil.
Reduce to a gentle simmer for 20 minutes, then remove from the heat and steep for 30 minutes.
Strain and Sweeten:
Strain through a fine-mesh strainer into a heatproof pitcher, pressing the bark lightly, then discard the solids.
Stir in the brown sugar while the concentrate is warm. Add the cold water, lime juice, and bitters. Taste and adjust sugar or water; mauby should keep a pleasant bitter edge.
Chill and Serve:
Cool completely, cover, and refrigerate for at least 2 hours.
Serve over ice with a thin lime slice.
Notes
Mauby bark strength varies, so dilute the concentrate to taste before adding more sugar.
The drink keeps refrigerated for five days; stir before serving.