In large skillet, heat peanut oil over medium-high heat.
Add onion and fry until soft, approx. 4 minutes.
Add garlic, ginger, and lemongrass and sauté a few minutes.
Reduce heat to medium.
Add scallions and curry paste and stir approx. 1 minute.
Add milk, broth, fish sauce, and sugar.
Bring to a boil and boil 2-3 minutes.
Add shrimp. Cook until shrimp are orange and opaque.
Garnish with cilantro, lime wedges on the side.