First thing first as always, get all your ingredients together. Dice your onion, decide how much seasoning you want in your burger meat, make a plan.

In a large bowl
Add the butter, melt it in the microwave. 15 seconds will probably do it.
Add the ground beef. Make a hole in the middle.
Crack the egg right in the hole you just made. Scramble it up a little with your finger, just so the yolk breaks and its a bit blended.
Add the A1 into the egg.
Add the seasonings to the meat around the egg.
Add the onion just like the seasoning.
Get your hands in there and smush and squeeze that mixture till it's a well blended meat mush.

Now you'll form your patties. 1 lb equals 4 nice thick burgers so try to get 4 even portions of the meat. Work it with your hands and form into patties. They should be about 3/4 inch thick.
Salt and pepper the completed patties.

Depending on how you like your burgers is how long you'll cook them. If you like them more rare, 3-4 minutes on each side. I like mine more well than rare so I did about 8 minutes each side.
VERY important!!
Don't puncture or press the patties!
You're covering them with a lid which does the job that you'd be trying to do by puncturing or pressing. Either one would also defeat the purpose of the sear. You sear to seal in the moisture and flavors.