In a blender or small food processor, combine avocado, sour cream, lime juice, garlic, and cumin. Blend until smooth. Season to taste with salt and serve.
Notes
For the smoothest crema with such a small volume of ingredients, use a mini food processor or immersion blender rather than a full-sized blender.
Press plastic wrap directly against the surface before refrigerating, not just over the top of the container. The crema will stay bright for up to 24 hours.