Slice the whole onions into half-inch thick slices.

In a large skillet or saute pan with high sides, melt the 6 tablespoons of butter over medium high heat.

Add the onions, salt and pepper and toss to coat then reduce the flame to low to medium low.

Toss occasionally while they slowly cook for about one hour. Set aside and drain and discard any liquid.

In a large bowl, tear the bread into small pieces then pour in the milk and mash with a fork. The bread and milk are not a binder but instead will help keep the mixture moist while cooking.

In the bowl of a food processor, add the raw bacon, onion, garlic, salt, pepper, thyme and the soaked bread and process until smooth.

Pour this back into the large bowl along with the ground pork and mix by hand.

Form into four patties the shape of the bread you are using and line up on a parchment covered tray that has been sprayed with kitchen pan spray.

Press your thumb into the center of each to make a large divot. When you cook these, the divot will stop the burger from mounding up in the middle and will cook flat. Place the patties in the refrigerator while you wait for the onions to cook.

When ready, heat one side of your grill to high and the other to medium.

Heat the cooked onions to hot.

Butter the bread on one side with the butter.

Clean then oil your grill and place the burgers, divot side down, on the hot side and the bread on the cooler side, butter down.

Cover each slice of bread with a slice of swiss cheese which will melt while the bottom browns and cover four of the slices with the drained onions.

Cook the burgers a few minutes on each side to an internal temperature of 150 degrees F. They will rise to 160 degrees F off heat.

If the bread has browned before the burgers are cooked, remove the bread to a sheet tray so they do not burn.

Place one burger over each pile of onions then top with the other slice of bread and serve.