Substitutions? What will happen if I leave out the parm, use vegan butter, and oat milk for the heavy cream?

I agree with the other comments. I haven’t used oat milk but have used almond and it worked great. Also the addition of nutritional yeast would be a great sub for the parm. Hope you enjoy!

I think it will be fine. You might want to add some nutritional yeast to taste to give you some of the umami that the parm provides.