In-N-Out burger - makes 6 burgers

So i've heard all these amazing things from people all round the world about these In-N-Out burgers in the states. As soon as i saw a picture of them on instagram i knew i wanted to try and recreate it. My friends Charlotte and scott who just got married (i was maid of honor woo!) went to america on their honeymoon and sent me a pic of the famous animal style burger... Here is my version

500g Beef mince 
20g Lard or dripping, into small chunks (I used this Wix Dripping) 
1 Tablespoon Butter
Salt and Pepper
1 Large Onion, chopped 
2 Tablespoons Mayo
1 Tablespoon Ketchup
1 Tablespoon Sweet Pickle Relish
1/2 teaspoon Sugar
1/2 teaspoon White Vinegar
​6 Hamburger Buns
12 Slices Tomato
Lettuce (enough for 8 burgers)
1/4 Cup Mustard
6 Slices American Cheese (I used coles smoked cheese singles)

Method:

Add the beef and lard together so the lard is distributed evenly thru meat, season well with salt and pepper and shape into 8 patties. Place in fridge to cool.
Heat 1 Tablespoon of butter in a non stick frying pan and heat until hot. Add onions and 1/2 teaspoon salt, reduce to a medium-low heat and cook until onions are brown (keep stirring and this could take up to 15mins).
Pre-heat oven to 200'c. Once onions begin to sizzle and appear dry and 2 tablespoons of water and mix. When onions seem dry add 2 more tablespoons of water, repeat again one more time until onions are soft and dark brown in colour. Once cooked set aside in a bowl.
To make burger sauce add mayo, ketchup, relish, sugar and vinegar to a bowl, mix well and place in the fridge.
Preheat same frying pan onions were in until preheated. Add the patties cook them for 2mins until brown and crusty on the bottom. While they are cooking spread mustard over the uncooked side. Flip the burger and cook for another 2 minutes or until cooked to your liking, add cheese to your burger just before removing from the pan so it can slightly melt .
Add the sauce to the top and bottom of the bun, add lettuce and tomato to the bottom of the bun. Top each burger with a patty and a generous amount of onions. Serve.