Heat half of the butter in a frying pan over a medium heat. Add the shallot, garlic and fry gently until softened - about 3-4 minutes. Add the watercress, peas, parsley and hot stock or water, bring the mixture to the boil, then reduce the heat until the mixture is simmering and continue to simmer for three minutes, or until the peas are bright green and just tender.
Pour in the cream, then blend thoroughly using a hand-held blender. Season, to taste, with salt and freshly ground black pepper, then stir in the remaining butter until melted.
Divide the soup equally among four serving bowls and garnish with the pea shoots, baby watercress, croûtons and crisp bacon pieces. Finish with a drizzle of olive oil. Serve immediately.