Serious Eats - seriouseats.com

I Take fresh ground chuck, and pinch off small pieces to make the bottom half of the burger, toss on some sea salt and FGP then flatten out all the little pieces into a burger shape. Them, take about a tablespoon of unsalted butter and divide it up into small 8 pieces and distribute them on top of your half-formed patty. Continue pinching of small pieces of beef and adding them to your burger until it is the size desired.

Your burger should have air, salt, pepper, and butter in all the little crevices and spaces that were formed by piecing it all together. Don't mash it all together(and squeeze out all that air), or else you'll get a moist hockey puck that tastes good. The butter and air pockets will help cook and baste the inside of the burger while it cooks. Dee-lish!