Cover the jar with a lid or cheesecloth and allow it to sit at room temperature for 24-48 hours.
Chill before serving. Keep sour cream in the refrigerator when not being consumed.
Notes
Homemade sour cream will be slightly thinner than store-bought sour cream. This is due to the lack of artificial thickness that is added to store-bought containers.
Buttermilk can be substituted for milk and vinegar.