Gently sauté the onion in the oil until soft, then add the peas. Cover and gently sauté for a few minutes, then remove it from the stove. Using a mini sieve or tea strainer, dust the flour all over it mix well then put it back on the stove and simmer for 1-2 minutes, whilst stirring.
Gradually pour in the vegetable stock or milk, while stirring constantly. Season with salt and pepper.
Cook at low temperature until it thickens to your liking (it shouldn’t be too runny but a custard-like sauce around the peas).
Serve hot with dollops of yogurt or sour cream.