TikTok user @Austin.Martinn has shared a number of videos to the platform, showing how things like the eggs are cooked, as well as preparing dehydrated onions at one of the chain's Canadian locations.
In one video, he shows himself cracking 12 eggs into a circular moulds on a grill, he then closes the top of the grill and pours water into the top of it to steam the eggs inside.
One user commented, "That's actually impressive, I just assumed it came in frozen packets?"
Another McDonald's worker added, "I can confirm the round eggs always come from actual eggs."
Someone else commented, "I didn't think they used real eggs."
The video has captivated the attention of a huge 1.2 million people so far.
Another video shows Austin rehydrating onion for the burgers, showing it comes dehydrated in a large packet that they empty into cups and add water.
The onions need to be soaked for an hour minimum, then drained of excess water and stored in the fridge.
While this might have come as a shock to some viewers, one said they didn't care how they were made, they still loved them.
"I don't care. I love those onions and want to buy some of those packs to make them at home," they wrote.
"It's dried so it can be preserved... nothing that surprising," another user said.
Others were shocked, "OMG I never knew this," one user said.
"Did not know onions could be dried like that. That's crazy," someone else added.
Another said, "[And] here I am at Subway, CRYING, slicing onions at 6am!"
Some said it would stop them from ordering onion on their burgers from now on.
Another user said they were 41 and that McDonald's had been using dehydrated onion since they worked there when they were 16.