Pull the needle off the rosemary sprigs, cut half of the chili into rings, and peel the garlic. No need to chop them finely.
Heat the olive oil in a small pan over medium-high heat. Add the rosemary, chili, and garlic and sauté for 3-4 minutes until lightly browned and softened.
Transfer the pre-fried aromatics to a bowl with mayonnaise and sour cream (or yogurt). Use an immersion blender to puree and whip everything into a smooth sauce. You can also do this in a food processor.
For courser texture, you can chop everything very finely with a knife. Taste for seasoning and add extra salt if needed.
