One of the Minecraft mods makes you actually do the video game equivalent (thus not over the correct time period) of how we actually get milk. Instead of just right click on any cow with a bucket (like vanilla Minecraft) that mod requires you to find a boy cow and a girl cow, ensure they're both happy (well fed, no nearby predators etc.), and after a short period nature takes its course and you get a baby cow. Next, steal the baby cow, you can kill it for food or just move it to somewhere mum can't reach it. She's recently given birth so her body will make milk but now there's no baby to drink it, so you can steal the milk.