Season the tilefish fillets with salt and pepper, then coat them lightly with flour.

Boil spinach in salted water for 1 minute, then drain and squeeze out excess water. Cut into thirds. Slice lemon into two thin rounds.

Heat vegetable oil in a pan over medium heat. Place the tilefish skin-side down and cook for 2 minutes. Flip, add sake, cover, and steam for 3 minutes. Remove from pan.

Wipe the pan clean, add butter, and sauté the spinach lightly. Plate the spinach and place the tilefish on top.

In the same pan, melt butter over low heat. Add sake, squeeze the remaining lemon juice, and season with salt and pepper. Mix well.