In a large bowl using a hand mixer or the bowl of a stand mixer fitted with the paddle attachment, beat cream cheese and sugar until fluffy and combined, 3 minutes.
Add eggs, one a time, until combined.
Add sour cream, flour, vanilla, and salt and beat until combined.
Pour filling into a SEPARATE 9' springform pan, use parchment paper to line it then bake until only slightly jiggly in the center, about 1 hour.
Let cool slightly, then transfer to the freezer to cool completely and firm up before assembling on top of the funfetti cake layer. Use a cake leveler again if needed/desired to achieve even layers.