Cut chrysanthemum greens into 4cm pieces and slice the onion.

Wash oysters gently in water 2-3 times, pat dry with paper towels, and coat with 1 tbsp flour.

Heat salad oil in a pan, add oysters, and cook over medium heat for 2 minutes until browned. Remove oysters.

Wipe the pan clean with paper towels, add butter, and heat until melted. Add onion and sauté over medium heat for 2 minutes until softened.

Add 3 tbsp flour and stir until combined. Add chrysanthemum greens and mix. Add remaining cream sauce ingredients and cook over medium-low heat until thickened. Cover and simmer on low heat for 2 minutes.

Return oysters to the pan and mix well.