When you pat out the "patties", press the center a little, so it is thinner, and you won’t have to cook it so long to get the center up to temperature. Also, you can put the meat in a bowl and add Worcestershire sauce to it before forming. Some even add a pack of onion soup mix.[:I]
Pressing the center will also help keep the middle from puffing up, especially when cooking on the grill. I first read about doing that in Cook’s Illustrated, and it really works!