In a large skillet, melt the butter over medium-low heat. Add the mushroom slices and coat both sides with the melted butter. Turn the heat up to medium-high and fry until golden brown. Remove from skillet and cut into bite-size pieces.

Season the steak with salt, pepper and garlic powder. In your oven, broil to medium-rare. Cool. Slice a few thin strips and set aside for finishing garnish. Cut the rest of the steak into bite-size pieces and place in a blender. Add the eggs and egg whites. Blend on high for about 30-45 seconds to further chop up the steak pieces.

Spray a medium-large non-stick skillet with vegetable oil and heat to medium-high. Add 2/3 cups of omelette blender mixture and spread out evenly to cover the bottom of the pan. If desired, season lightly with salt and pepper. Cover skillet and turn heat down to medium. Cook until set, about 5-6 minutes.

Distribute 1/4 of the mushrooms over half the omelette, fold in half and slide from the skillet onto a cookie sheet. Keep warm in oven, set to lowest heat, while preparing the remaining omelettes.

Prepare the béarnaise sauce. Plate each omelette, top with sauce, and garnish with the reserved steak slices and minced chives.