Slice the onion thinly. Trim the spinach roots, wash thoroughly, and cut into bite-sized pieces.

In a bowl, mix oysters with cornstarch and gently wash with water until clear. Drain and pat dry with paper towels.

Boil macaroni for 1 minute less than the package instructions, then drain.

Heat 10g butter in a pan, add oysters, and cook until browned. Flip, cover, and steam for 1 minute on low heat. Remove from pan.

Wipe the pan clean, heat 20g butter, and sauté spinach and onion until onion is translucent. Add flour and stir until no raw flour remains. Gradually add milk, stirring until thickened. Season with salt, then add oysters and macaroni. Bring to a boil.