For the green beef curry, heat oil in a saucepan, add curry paste and fry over medium heat for about 5 minutes until intensely fragrant. Add the meat and fry. Add the lemongrass, kaffir lime leaves and white onions, continue to fry until the onions are translucent. Deglaze with the water, bring to a simmer over low heat.
Mix young onion greens with coconut milk and puree with a hand blender, add to stew along with sweet potatoes and salsify. Cook for about 20 minutes, add broccoli. Season stew with fish sauce, lime juice, sugar and salt and simmer for another 10 minutes.
Dressing: Sprinkle the white part of a young onion cut into fine rings or freshly cut cilantro over the dressed stew. The green beef curry goes well with a simple Thai fragrant rice.