Introduction: Cheeseburger Picnic. I decided to throw a party for my friends the other day. The idea was that I was going to provide as many cheeseburgers as they could eat, but anything else they wanted they had to bring themselves. This resulted in my making an absurd amount of cheeseburgers from scratch, but I documented the whole process and the pictures turned out nice so I thought this would be a good icebreaker for my first Instructable. 
I'm not all that conventional when it comes to food.  I do things that often take too much time and generally don't save me any money, like making things from scratch and sourcing the best quality ingredients for the recipes and meals that I make, but in the end the food speaks for itself and I think some of my friends just enjoyed the best hamburgers of their life.What you will need:
Ingredients:
-Beef Sirloin or round roast or blade roast or any mix of them
-Pork butt or shoulder
-Seasonings to your taste (Worcestershire sauce, soy sauce, salt pepper, granulated garlic, etc..) 
Equipment:
-Meat grinder Step 1: Your Meat. I got my meat from a store that procures local meat I was happy with the freshness and the price. The difference in this and regular hamburger is significant in price (apx. $7/lb vs $2/lb regular ground beef), but the result is undeniably superior quality.
For the best burgers you want fairly fatty cuts such as sirloin or blade, but you can tweak with your flavours by adding some stronger flavoured cuts in as well such as flank or anything you would usually stew with.  I also use pork shoulder or butt in my burgers, it's not necessary but it's part of what makes my burgers the best I think.
I like a ratio of 3:1, beef:pork Step 2: Trimming and Seasoning. I trim my meat from the bone (reserve for stock), and with the pork I also try to get as much of the skin off too, but I leave as much fat as I can.  I cube all of my meat into roughly 2" cubes to accommodate my grinder. As I cube my meat I layer it in my bowls and I season each layer (I use a healthy amount of Worcestershire and soy sauce and garlic powder).  I really don't like to add much in the way of seasoning because it will take away from all of the amazing meat flavours, and we're making burgers here, not meatloaf.
I let this sit in a freezer for 2 hours or so to keep chilled for food safety reasons and to aid with grinding as somewhat frozen meat grinds so much nicer than the alternative.  Step 3: The Grind. The grinding is straight forward. I really prefer a course grind for these burgers, the texture is meaty instead of paste like this way.  All I do is try and keep my 3:1 ratio and I roughly mix the cubes up in the hopper so they grind kind of evenly.  You want to blend everything before hand so you're not overworking your meat after it's ground, otherwise run the risk of pasty overworked meat. Step 4: The Burgers. I'm not sure what my patties weigh, but I grab a handful of the ground meat mixture slightly smaller than a tennis ball and I loosely form it into a uniformly thin patty, trying not to overwork it. If you keep a bowl of water to dip your hands into occasionally you will notice that the meat and its fat won't stick to your hands making everything much more workable, especially when you're trying to put your patties from your hand onto whatever surface you've chosen to amass them on.  
I made 120 patties  Step 5: The Grill. Just throw them on a hot grill.  Don't squeeze or press any juice out of them and only flip them one or twice if you can. Melt your favourite type of cheese on them just before serving and toast up some buns for these flavour monsters.
A trick I like to use to melt the cheese quickly is to toss a cast iron pan upside down over the burgers to trap some heat over them
I think next year I might do a BYOCheese cheeseburger party to get a nice diverse range of flavours Step 6: The Eating. Simply dress to your liking and enjoy