Put the vegetable stock in a large saucepan over a high heat and bring it to a rolling boil. Add the peas and simmer for 8-10 minutes or until tender. If using frozen peas cook from frozen and simmer for about 5 minutes.
Meanwhile mix the ricitta and lemon zest together in a small bowl.
Once the peas are cooked remove the pan from the heat and stir in the cream and most of the mint leaves. Blend in a blender or food processor, then season to taste with salt and pepper.
Divide the soup between four bowls and serve each topped with a tablespoon of the lemon ricotta and a few of the reserved mint leaves sprinkled over.