Add butter to the pan. After the butter has melted, pour in the eggs. Cook, lifting edges to let uncooked egg run underneath and shaking skillet occasionally to loosen omelet, until almost set. Add the Feta cheese and pancetta-mushroom mixture. Fold and slide out onto a large plate. Sprinkle with Feta and chives.
Recipe by Sugar and Spice at https://kathleenssugarandspice.com/2011/03/04/award-winning-omelet-pancetta-sauteed-mushrooms-feta-cheese-chives/