Heat cream gently to 75–80°F in a clean pot.
Stir in mesophilic starter or buttermilk. Add rennet if using.
Cover and culture at room temperature for 12–18 hours, until thickened like yogurt.
Pour curd into a cheesecloth-lined strainer over a bowl and drain 6–12 hours, until desired thickness.
Mix in salt and whip with a spoon, food processor, or hand mixer until smooth.