Put the heavy cream in a 16-ounce microwave-safe glass jar. Microwave on high until the cream is just under 100ºF, 30 to 40 seconds. Add the buttermilk, close the jar, and store in a warm place for 24 hours. The cream will have thickened to the consistency of thin yogurt.
Add the chipotle chile and salt, and process with an immersion blender, in the jar, until smooth, approximately 20 seconds. Refrigerate until ready to use.