Season the fish with salt and pepper.
Fry the fish skin-side down in olive oil until crisp, then flip and finish with lime juice.
Stir-fry the beansprouts, mushrooms, and mangetout in sesame oil.
Mix the toasted sesame seeds into the softened vegetables.
Sauté shallots and lemongrass in half the butter.
Add fish stock and reduce the liquid by half.
Reduce the white wine in a separate pan by one third and add to the stock.
Stir in the cream, bring to a boil, then simmer until slightly thickened.
Strain the sauce through a sieve and whisk in the remaining butter.
Serve the fish over the vegetables and drizzle with sauce.