With top notch existing technology (need not be currently industrially used, existing research application sufficient) and no regard for (external) ecology, economics or politics, we'll build a structure on Earth that houses the sustainable (sustainable not in the woo woo 'don't hurt Gaia' sense, but meaning any means that can be sustained for an unlimited amount of time) means of human foodproduction. Not -distribution (apart from 'out'), though.
Assume readily available electric energy. Global veganism if need be.
Scale as required (if full or part synthesis is possible, go for it). Structure needs to not be scattered, but can be any topology and form engineerable. Structure can float, be underground, anything. Thermal regulation needs to be taken into account.
Hydro- and other -ponics essentially go from N2 and CO2 to sugars, fats and protein via biochemistry driven by photosynthesis. There might be a way to create some of that in bulk via industrial synthesis, bypassing the volume -inefficient flora.
How many cubic meters of structure per person, minimally?