Step 1

Heat the butter in a large pot over medium-high heat. Add the onion and cook for 3 minutes, or until it is translucent and soft. Add the garlic and cook for 1 minute more.

Step 2

Add the asparagus, potatoes, and stock to the pot and bring it to a boil. Reduce the heat to medium-low, cover the pot, and simmer for 15 minutes, or until the potatoes are soft.

Step 3

Add the spinach (if using) to the pot then blend the soup either with an immersion blender or carefully in small batches in a blender. Season to taste with salt and pepper. If using, stir in the lemon juice.