1. Begin by slicing the bacon in half, then into 1/8" strips. Turn the bacon around and cut into 1/8" pieces. Place the bacon in a Teflon fry pan, on medium heat, and cook until the bits have rendered all of their fat. Be careful that you don't let the bacon burn.
2. While the bacon is cooking, place the butter into a small pot over medium heat and let the butter melt.
3. While both are cooking, place 4 egg yolks into a blender with the lemon juice, and blacken and blend until smooth.
4. When the bacon is done, add it and the bacon fat to the egg yolks and blend quickly until the bacon has been all chopped up. With the blender running, slowly pour the hot melted butter in. The hot butter and bacon fat will cook the eggs.
5. Serve hot or at least real warm. If you wish to store this, or prepare it ahead of time, be sure to place plastic wrap directly on the sauce, or it will develop a skin.
6. If you would like to serve this sauce as a rich dipping sauce, you'll probably want to thin it down with a little milk or orange juice.