Preheat the oven to 450°. Pat the artichoke hearts dry with paper towels and halve them lengthwise. Arrange the artichoke hearts cut side down on a lightly oiled baking sheet and roast for 5 minutes, until sizzling. Carefully transfer the artichokes to a plate. Arrange the celery leaves on the baking sheet and coat with the reserved artichoke oil. Roast for 3 minutes, until the leaves are crisp.