Sforno on Exodus 16:5/ספורנו על שמות ט״ז:ה׳

1והכינו את אשר, even after having prepared the food from the raw manna it will still be twice the quantity it had been on the previous days. It will not shrink in the course of preparation. The reason G’d speaks of והכינו, “they will prepare it,” is to encourage the people to prepare for the Sabbath by observing it with delicacies, especially tasty food. They should concentrate on all this on the Sabbath eve.