Refrigerate the unopened can of coconut milk overnight so the cream rises to the top.
Open the can without shaking it and spoon the thick cream into a clean glass jar, leaving the clear liquid behind.
Whisk the cream until completely smooth.
Stir in the vegan yogurt or probiotic capsule contents until evenly mixed.
Cover the jar loosely with a cloth or coffee filter secured with a rubber band.
Ferment in a warm spot (75 to 85°F) for 12 to 24 hours, until tangy.
Stir in maple syrup and vanilla if using, seal the jar, and refrigerate. It thickens as it chills.