Pesto lasts longer with olive oil
I like to buy some larger pesto glasses, as they are cheaper than several small glasses.
To enjoy the pesto to the last spoon, without it dries or molds, I drip a little olive oil on the mass, before I put it back in the refrigerator.
Just stir well before using and of course always use a clean spoon.
With homemade pesto, of course, you do the same.