Green pea and Spinach soup

Ingredients

1 teaspoon olive oil
1 large onion, sliced (about 1 1/2 cups)
2 1/2 cups veg stock 
1/2 teaspoon salt
2 tsp black peppercorn
250 gms green peas
400 gms Spinach
4 teaspoons plain  yogurt, 

Directions

In a large pot, heat the olive oil over moderately-low heat. Add the onion, cover and cook, stirring occasionally, until softened, about 5 minutes. Add the stock  and  black pepper and bring to a boil. Add the peas ,spinach  and cook just until it gets soft. Finish with yogurt.

In a blender, puree the soup in  until very smooth.