For the Ragu: In a saucepan, render the pancetta over medium heat, about 8 minutes, or until almost all the fat is rendered. Season the beef with salt and pepper. Add the beef to the pancetta and brown the meat for 5 minutes, or until the meat is medium brown in color. Stir in the carrots, celery, and onions. Season with salt and pepper. Saute the vegetables for about 5 minutes or until the vegetables are translucent. Dilute the tomato paste in 1/2 cup of water. Stir in the garlic, wine, diluted tomato paste, stock and tomato sauce and reduce the heat to very low. Cook, partially covered, for 2 hours.
For the Pasta: In a mixing bowl, combine the potatoes, butter, cheese, egg and peppermint oil. Season with salt and pepper. Add in enough flour to form into a smooth ball. Cover the dough and allow to rest for 30 minutes.
For the Cheese Filling: In a saute pan, over medium heat, add the oil. When the oil is hot, add the Swiss chard. Season with salt and pepper. Saute for 2 minutes. Remove from the heat and cool. In a mixing bowl, combine the Swiss chard, cheese, eggs and nutmeg. Mix well. Season with salt and pepper.
To assemble: Divide the dough in half. Lightly dust a work surface with flour. Roll both of the dough's out into a rectangle, as thin as possible. On one of the sheets of pasta, place heaping spoonfuls of the cheese mixture about every 2 inches. Place the other sheet of pasta over the first sheet of pasta and press down firmly around the mounds of cheese. Using a knife or pastry wheel, cut between the rows to make 1 1/2-inch squares.
Bring a pot of salted water to a boil. Add the ravioli and cook until tender, about 4 to 5 minutes. Drain and toss with the olive oil. Season with salt and pepper. To serve: Place a quarter of the raviolis in each serving bowl. Spoon the ragu over the pasta.