Can one use a pressure can of whipped cream on shabbas ?
It is funny because on the actual can it says to ask your Rabbi if one can use it or not.
Rav Daniel Mann based on Rabbi Mordechai Willig says it is permitted.
The most serious issue is molid, creating a new reality by changing the phase of an object. The baraita (Shabbat 51b) forbids crushing ice and snow. Rashi explains that it is like a melacha, in that one creates something new, i.e., a liquid from a solid. Some say that, similarly, one may not turn a liquid into a solid, e.g., freeze water to make ice cubes (see Doveiv Meisharim I, 55). We dealt with this issue in Hemdat Yamim (Miketz 5767), and cited strong grounds for leniency. Orchot Shabbat (15:(45)) says that even those who forbid making ice cubes could permit spraying whipped cream from a canister because the only purpose of the cream in the canister is to be turned into whipped cream. On the other hand, here one actively and directly, with the press of the button, creates the foam, as opposed to putting water in a freezer, which only provides a cold setting for the slow process of freezing to begin (see Shemirat Shabbat K’hilchata 10:(14)). However, Rav Mordechai Willig told me another reason for leniency: the change, from a thick liquid to a foam, is not enough to be considered molid. While one can make the argument that it is forbidden to spray whipped cream from its canister, common practice is to permit it. Since we have shown the halachic basis for the practice, we do not feel it is necessary to change it. (We have not dealt with the issue of using the cream to write words or make likenesses of specific objects.)
I saw in the Rivevos Ephraim chelek 8:158:11 a few shittos on this topic asked by a bachur to the gedolim. Rabbi Goldstein assurs it because of nolad,also in the sefer Hilchos shabbas in the kitchen pg.961 Rabbi Menashe Klein,Rabbi Moshe Stern(Be'er Moshe) and Rabbi ראטה(not sure which one) hold the same opinion.
Rav Scheinberg,Rav Fisher,Rav Dovid Feinstein held its mutar,also Rav Belsky(see lamed tet Mahlachos hilchos dosh footnote 176a for a different savarah or opinion).See it inside.
The sefer Rishumei Ahron chelek 2:pg 30:3 brings down the opinion of Rav Moshe that there is no issur of nolad by a whipped cream aerosol can.
It says on Halachipedia.com
It is forbidden to use whipped topping or whipped cream from a can on Shabbat. 
Halachipedia's sources: ↑ 39 Melachos (vol 2, pg 371), Halachically Speaking (vol 4, Issue 16, pg 5) quoting Rav Yisrael Belsky