Before You Begin
Preheat and prepare your cookware as needed. Cooking and blending times may vary depending on equipment and ingredient thickness.
Heat butter and olive oil in a large pot over medium heat. Add onions and cook until softened and lightly golden.
Stir in garlic and red pepper flakes and cook briefly until aromatic.
Add asparagus, broth, thyme, salt, and pepper. Bring to a gentle boil, then reduce heat and simmer until asparagus is very tender.
Blend the soup until smooth using an immersion blender, or blend in batches in a regular blender, allowing steam to vent safely.
Return soup to low heat. Stir in Parmesan, dill, basil, lemon juice, and Greek yogurt.
Taste and adjust seasoning as needed. Serve warm.
