Mince the Beef, Pork and Pork Fat together and refrigerate. Measure the mince into 67g balls. Flatten to 100mm in diameter and set between baking paper sheets. Then freeze.
Combine the Tartare sauce and Thousand Island dressing together and refrigerate. Update:: Use Heinz Hamburger sauce and chop in some extra pickles.

Less is more with the bun. The small brioche bun is not precut. Slice into 3 even layers.
Take 4 top buns and brush with whisked egg white. Sprinkle with sesame seeds. Grill 40 seconds
Sit the frozen patties on the bench for 10 minutes before cooking
In a non stick frypan cook the patties 2 mins. Mop off excess moisture before turning and cook a further 2 mins. Push down with a spatula. Sprinkle with MSG. Set on tray in a 110deg oven for >15 mins.
Toast the buns to a light brown.

Assembly:: Put 1 Tbs of sauce on the bottom bun and 1 Tbs of sauce on the middle bun. Then sprinkle each with the onions and add shedded lettuce. Put the cheese slice over the lettuce on the bottom bun and the pickles over the lettuce on the middle bun. Add a patty to each. Compress with your hand. Put the middle bun assembly on the bottom assembly and finish with the top bun. Ideally stand in a warm oven for a few minutes.
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I miss the days of the pre made burger sat in a polystyrene container under heat lamps. It was actually a better product. Freshly made in a cardboard box did nothing.

Tip top hamburger buns are too big, Mighty soft have a bun that's about right and Woolworths sell small brioche buns that are great. The ratio of bun to burger is critical. Less is more.

I mucked around for quite a while and without adding a pinch of MSG I could not get that opening of the cheek glands that you get after eating a Big Mac. And that is in fact the most crucial element of why a Big Mac is so addictive. You eat the burger and are left with a salivating palate that locks in your brain for future reference "I want another." The constant marketing campaigns, product placements, childhood memories and subliminal images brainwash you into craving another. Every time you drive past the Golden Aches your brain reacts and your palate salivates. Till one day you can't resist and you dangerously swerve across 3 lanes of traffic, mount the pavement, scatter pedestrians and cut ahead in the drive thru to get that craving satisfied. It's that addictive. Just saying.

Truly, one of the very best recipes of all time matched with relentless marketing.

250g Chuck Steak
200g Pork Butt
100g Pork fat

80g Tartare sauce
80g Thousand Island dressing

4 small Brioche Buns
2 Tbs sesame seeds
4 Tbs finely chopped onions 
2 leaves of Shredded Iceberg Lettuce
4 Processed Cheese slices
12 Bread and Butter Pickles

Pinchs MSG
Pinchs Salt
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The original is an all beef patty and you can. You will need 20% or more beef fat. I believe that my patty is actually closer to the original in taste and texture. The pork fat really adds the correct flavour and ups the umami. It must be well done and then well rested. You might think a nice medium rare patty could be better, but it isn't. Recently I picked up 6 bottles of Original Big Mac Sauce
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Recent variation:: Pretty pretty good
Double cheese and pickles, no onion

Make the top and bottom the same. Omit the onion and put pickles and a cheese slice on both. Chop extra pickles into the sauce.

Lets not kid ourselves. Everyone that says they hate Macca's and its burgers are gross are really just projecting "I sneak through the driveway at a store remote to me and secretly eat a Big Mac every so often". Its just a fact. Even vegetarians do it. And I agree, there are better hamburgers, far more satisfying fast foods, much healthier options and every other myth closet eaters can come up with. So then why is it so addictive.

I say it is without doubt one of the great recipes of all time. And here is why. Taste, Texture and Umami in exactly the right ratios. How do I know this. I have cooked 30 different versions of a Big Mac at home. Almost all failed because a single element wasn't like a Big Mac. Too thick a patty, quality cheese off the block, too much or too little sauce, too big a bun, medium rare patty, no sesame seeds etc. But I am persistent and its with pleasure I give to you my version that does, ever so slightly, (maybe not) better an original Big Mac.

The Brioche Bun is better, the simple sauce is really close, the patty is tastier and the rest is the same.