Sauté the aromatics: Heat the oil in a large pot over medium heat. Add the onion (or shallots) and cook 2–3 minutes until softened. Stir in the garlic and ginger for 30 seconds, just until fragrant.
Bloom the curry paste: Add the green curry paste and cook 1 minute, stirring.
This step wakes up the spices and deepens the flavor. If using lemongrass, add it now.
Build the broth: Pour in the broth and bring to a gentle simmer. Stir in the coconut milk, fish sauce (or soy/tamari), and sugar.
Taste and adjust salt now so the base is balanced.
Add protein: Slip in your chicken, shrimp, or tofu. If using chicken, simmer 6–8 minutes until just cooked. Shrimp needs about 3–4 minutes.
Tofu can simmer 5 minutes to absorb flavor without breaking apart.
Add vegetables: Stir in vegetables and simmer 3–5 minutes until tender but still crisp. You want color and bite, not mush.
Finish with lime: Remove lemongrass (if used). Add lime zest and squeeze in lime juice to taste.
The citrus should brighten the whole pot.
Serve: Ladle into bowls over warm rice or rice noodles, or serve as-is for a lighter soup. Top with herbs, scallions, and chili slices if you like extra heat.