Prepare the Asparagus: Wash the asparagus thoroughly and trim off the tough ends. Cut the asparagus into 2-inch pieces, discarding any woody parts.
Sauté the Onion and Garlic: Heat a large soup pot or pan over a medium heat and spray it with low-calorie cooking spray. Add the onion and garlic and sauté for about 2-3 minutes until the onion becomes translucent and fragrant.
Add Potatoes and Asparagus: Add the diced potatoes and asparagus to the pot and stir well with the onions and garlic.
Pour in the Stock: Pour in the vegetable stock, ensuring that the potatoes and asparagus are submerged. Bring the mixture to a boil.
Simmer: Reduce the heat to low, cover the pot, and simmer for about 15-20 minutes or until the potatoes and asparagus are tender.
Blend: Using an immersion blender, carefully blend the soup until it's smooth and creamy. If you don't have an immersion blender, you can transfer the soup in batches to a blender, but be sure to let it cool slightly before blending to avoid splattering.
Add Milk: Return the blended soup to the pot, and stir in the skimmed milk. Cook for an additional 5 minutes over low heat, stirring frequently.
Season: Season the soup with salt and black pepper to taste. Adjust the seasoning as needed.
Serve: Ladle the hot soup into bowls. Garnish with chopped fresh chives if desired.