Chop spring onion white bulbs and green leaves separately.
Melt butter in a pot, sauté garlic paste and spring onion whites for 2 minutes.
Pour in vegetable broth, soy sauce, black pepper, and salt; bring to a boil.
Mix cornstarch with 2 tbsp cold water, pour into soup while stirring to slightly thicken.
Stir in chopped green spring onions and serve immediately.