You may need to modify this in a post-event world as a microwave oven might not be working...
First, grow your sugar beets... Wait 'til they ripen...
You can do this in a wood fired oven or a solar oven. The times will vary.
https://www.leaf.tv/articles/how-to-make-sugar-from-beets/Bake
Mash
Simmer, not boil
Filter and keep liquid. Feed the mash to cows.
Dehydrate to get crystals
Store in airtight jars