In a medium Dutch oven, heat oil over medium heat. Add onion, celery, garlic, salt, and pepper; cook until fragrant, 3 to 4 minutes. Add broth, herbes de Provence, paprika, and garam masala; bring to a boil. Stir in peas and watercress. Reduce heat, and simmer for 20 minutes, stirring occasionally. Remove from heat; using a hand blender, blend until smooth. Serve warm.
Just before serving, place sour cream in a piping bag fitted with a large open-star tip (Wilton #1M), and pipe a rosette onto each soup spoon, if desired. Garnish individual servings with watercress, if desired.
Recipe by TeaTime Magazine at https://teatimemagazine.com/watercress-pea-soup/