Saute the chopped onion in butter and olive oil.
Add the chopped potato and sliced garlic.
Season with salt, pepper, and turmeric.
Deglaze with white wine.
Add the chicken stock and bay leaf, then simmer for 20 minutes.
Cube the sourdough bread, toss with olive oil and salt, and toast in the oven until golden.
Assemble the soup with the toasted bread on top, add cheese, and broil for a few minutes.
Top with parsley.
