Once the oil is medium-hot, add chopped onion. Fry till it softens.
Add minced garlic. Saute them until they become aromatic (avoid burning).
Add chorizo chunks. Cook for 4- 5 minutes. It will start to release oil and the color will change.
Add and cook potatoes in stock
Add cubed potatoes. Cook on medium heat for 5-7 minutes.
Add cumin powder, and thyme and season with salt. Mix well.
Add chicken stock and bay leaf. Let it come to a boil, then, reduce the heat to low. Cover and let it simmer for 15 minutes or so until the potatoes are cooked.
Stir in between. If required add more stock. Potatoes should be cooked and become soft.
Add milk and simmer
Once the potatoes are cooked through, add milk.
Stir well. Cover and let it simmer for another 10 minutes on low heat.
While serving, garnish with chopped green onion.
Notes
The chorizo is spicy enough, so I have not added any chili powder. You can adjust the spices as per your preference.
If you want to reduce the cooking time, substitute raw potatoes with cooked potatoes.
I prefer to have small potato chunks in the soup. If you prefer something very creamy and thick without any chunks, use a blender to blend everything in the soup after the potatoes are cooked. This will make the soup very creamy and smooth.