Place a large pot of salted water over high heat. Add the diced potato to the pot of water and allow the potato to cook while the water comes to a rolling boil. Remove the diced potato to a blender when a fork easily pierces the flesh.
Meanwhile, place a large skillet over medium heat. When the skillet is hot, add 1 tsp olive oil and swirl to coat. Sear the Lemon & Herb Daring Pieces for 5-6 minutes on each side, or until golden brown and completely cooked through. Set the Daring Pieces aside on a clean plate and reserve.
Wipe out the skillet with a paper towel and turn heat to medium-high. Add the remaining 2 tsp olive oil to the skillet, along with the yellow onion and garlic. Season with ½ tsp salt and sauté the mixture until the onions are softened and translucent, around 5-6 minutes.
Add the sautéed onion and garlic mixture to the blender with the boiled potato, along with the non-dairy milk, nutritional yeast flakes, vegan butter, remaining 1 tsp salt, lemon juice, black pepper, and cornstarch. Blend for 15-20 seconds, or until completely smooth.
Pour the blended sauce into a large, high-walled skillet or dutch oven and bring to a gentle simmer over medium heat, stirring frequently, until slightly thickened.
Meanwhile, add fettuccine to boiling water and cook 2 minutes shy of al dente, according to the package instructions. Reserve 2 cups of starchy pasta water, and drain the fettuccine.
Add the drained fettuccine to the simmering sauce and cook, tossing frequently, for 3-4 minutes, or until the pasta has soaked up a fair amount of sauce and is completely tender. If the pasta begins to look dry, add splashes of pasta water as needed.
To serve, divide the Fettuccine Alfredo among 4 bowls, and top each with a generous portion of seared Daring. Pour any remaining sauce over the top of each bowl, and garnish with plenty of black pepper and chopped fresh chives, if using.