Yoma 49B

כיצד הוא עושה? אוחז את הבזך בראש אצבעותיו, ויש אומרים בשיניו, ומעלה בגודלו עד שמגעת לבין אצילי ידיו, וחוזר ומחזירה לתוך חפניו, וצוברה, כדי שיהא עשנה שוהה לבוא. ויש אומרים: מפזרה, כדי שיהא עשנה ממהרת לבוא.

How should the High Priest act in the Holy of Holies, when he needs to place the incense on the coals by taking a handful from the spoon and placing it in his hands? After he places the coal pan on the ground, he holds the front of the ladle, i.e., the spoon of incense, with his fingertips, and some say he holds it with his teeth. At this stage the handle of the spoon rests between his arms. And he pushes it and raises it up slowly with his thumb toward his body until it reaches between his elbows, which he then uses to turn it over. He then returns the incense into his palms, after which he pours it from his hands into the coal pan. And he heaps the incense into a pile on the coals so that its smoke rises slowly. And some say he does the opposite, that he scatters it so that its smoke rises quickly.

וזו היא עבודה קשה שבמקדש. זו היא ותו לא? והא איכא מליקה! והא איכא קמיצה! אלא: זו היא עבודה קשה מעבודות קשות שבמקדש. שמע מינה: חופן וחוזר וחופן. שמע מינה.

And this taking of a handful of incense is the most difficult sacrificial rite in the Temple. The Talmud asks: This one is the hardest rite, and no other? But there is pinching, which is also considered extremely difficult; and there is taking a handful of a meal-offering, another complex rite. Rather, this taking of a handful of incense is one of the most difficult rites in the Temple, rather than the single most difficult one. In any event, you can learn from this that the High Priest scoops a handful and again scoops. The Talmud concludes: Indeed, learn from this that it is so.