At first glance, the Latin verb pa:sco appears to be one of your usual *ske/o presents. This, however, is not the case; one can tell by the lengthened grade of the root. Normally the *-ske/o- suffix is added to the zero-grade of the root, which would thus yield pasco, with a short 'a' < *ph2-sko instead of *peh2-s- > pa:sco. According to the Etymological Dictionary of Latin by Michiel de Vann, the -sc- in the Latin verb is an "enlarged variant of the 's-present'", this s-present being formed from the root *peh2- 'to protect'. How this 'enlarged variant' comes about, I do not know.
s-presents usually have a desiderative meaning, that is, they express desire or intent. That -sc- is a desiderative suffix on the root *peh2- makes some semantic sense; *peh2-s- would mean 'to want/intend to protect', which leads us to the meaning of pasco in Latin, namely 'to feed, nurture, nourish'
Now I wonder how many other verbs which show this 'enlarged variant' there are.
As a random aside: this series is fantastic. I can't wait for the Greek one which Beekes is preparing to come out.