01 - Heat butter and olive oil in a large pot over medium heat. Add chopped onion and cook 3-4 minutes until soft and translucent.
02 - Stir in minced garlic and cook for 1 minute until fragrant, being careful not to brown.
03 - Add diced potato and asparagus pieces. Cook for 2-3 minutes, stirring occasionally to lightly coat in fats.
04 - Pour in vegetable broth and bring to a boil. Reduce heat, cover, and simmer for 15 minutes until vegetables are completely tender.
05 - Remove from heat. Puree with an immersion blender until completely smooth, or work in batches using a countertop blender.
06 - Return soup to low heat. Stir in heavy cream, lemon juice, and lemon zest. Season with salt and pepper to taste. Heat gently until warmed through without boiling.
07 - Ladle into bowls and garnish with fresh chives or dill. Add an extra squeeze of lemon juice if desired. Serve hot.