"We got an email from someone about an American place where they had this massive burger ... so we thought we should try and make that burger ourselves."
They then hit the first hurdle - where to get buns big enough. Their local bakery solved the problem, fashioning a prototype about three times as wide as even the largest available at most takeaway shops.
Measuring 19cm across, the bun itself is enough to scare off many customers who ask the Jouberts exactly what they mean by Jumbo.
What goes between reads like a typical family grocery shopping list - half a lettuce, a whole chopped tomato, three fried eggs, two large slices of shoulder bacon, three or four gherkins, a quarter of an onion, mustard, tomato sauce and a special cheese sauce that flows down the sides of the beast.
The burgers are two 180g patties that, hefty as they are, are placed alongside each other rather than stacked. One of its patties constitutes 30.6g of fat - nearly 5g more than that of an entire Big Mac.
Carl Nelson holds the honour of being the first person to eat the entire stack. He was a teenager working at the store at the time and accepted a challenge that he wouldn't be charged if he could finish the heap in one sitting.
Over the busy summer season, the shop sells about 10 of the $20 burgers each week, and Mrs Joubert guessed that about only half were finished.
"It's not a big seller, just mainly a fun thing, and it's all mainly big guys who order it," she said.
The record for the biggest burger commercially available goes to Juicy's Outlaw Grill in Corvallis, Oregon, for a burger weighing 352.44kg, which costs $6000 and demands 48 hours' notice to prepare.