In a saucepan, bring 3 1/4 cups water (750 ml) to a boil with the lemongrass. Reduce the heat and let it steep for 15 minutes.

Add the fish fillets to the water and cook over medium heat for 10 minutes. Once cooked, drain the fish, reserving the broth. Let the fish cool.

Boil the potatoes for 20 minutes. Once cooked, peel them.

Mash the potatoes and fish together with a fork. Add 2 tablespoons of the reserved broth, the heavy cream, butter, salt, and pepper. Mix well.

Heat sunflower oil in a saucepan. Shape the fish and potato mixture into balls. Roll them in breadcrumbs and fry until golden brown. Once cooked, place them on a plate lined with two paper towels to drain excess oil.