In a large pot over low heat, slowly cook the onion in 3 Tablespoons olive oil until it is translucent and tender. Season the onion with salt and pepper. In a separate saucepot bring the stock to a boil and keep hot. Add the orzo pasta to the onions and mix thoroughly. Gradually add the stock to the pasta and cover completely. Cook the pasta at a low simmer and stir carefully to avoid sticking.
In a large sauté pan heat 3 Tablespoons olive oil and sear the mushrooms and garlic scapes until golden brown. Add the butter. Let the butter become golden brown, then strain the mushrooms and scapes and reserve. In a cold bowl, whisk the heavy cream until slightly thick.
3. Cook the pasta until it is firm to the bite. Finish the pasta with truffle butter, Parmesan cheese, and the baby arugula. Add the heavy cream at the very end before serving. In a large bowl spoon the pasta into the center and place the mushrooms and scapes over the top. Shave a block of Parmesan cheese with a potato peeler to get thin shavings, and use them to garnish the dish.