Heat olive oil in a saucepan over medium heat. Cook and stir serrano peppers, garlic, and ginger in the hot oil until fragrant, 15 to 20 seconds. Add onion; cook and stir until softened and transparent, 10 to 15 minutes.
Mix potatoes into onion mixture and cook for 2 minutes. Add cabbage and cook for 2 minutes more. Pour chicken stock over cabbage mixture; bring to a boil. Reduce heat and simmer until potatoes are softened, 10 to 15 minutes. Season soup with garam masala and salt.
Pour soup into a blender no more than half full. Cover and hold lid down; pulse a few times before leaving on to blend. Puree in batches until smooth. Return soup to saucepan and cook until warmed, 2 to 3 minutes.