It is possible to smooth PLA using ethyl acetate, but I don’t know if that’s good enough for food safety, plus you have to remove the ethyl acetate itself.

PLA won’t survive in a dishwasher. PETG might, but there are no reasonable solvents for smoothing PETG.

Maybe it’d be best to print a mold in PLA, smooth with ethyl acetate, clean thoroughly, and then pour silicone into the mold.