Gather all ingredients.

Combine milk and vinegar in a small bowl; set aside for 10 minutes.

Pour heavy cream into a jar. Stir in milk-vinegar mixture. Cover jar loosely with cheesecloth to allow mixture to breathe and coagulate; let stand at room temperature for 24 hours. Chill before using and store leftovers in the refrigerator in a covered container for up to 1 week.