Heat oil and butter in large pot.
Add onions, celery, and bell pepper.
Cook for 5 minutes until softened.
Add garlic and cook 1 minute more.
Stir in paprika, cayenne, and thyme.
Add diced potatoes and chicken broth.
Bring mixture to a boil quickly.
Reduce heat and simmer 20 minutes.
Potatoes should be fork-tender now.
Remove bay leaf from pot.
Blend half the soup if desired.
Stir in heavy cream gradually.
Season with salt and pepper.
Garnish with green onions before serving.