Pour boiling water over the cashews and let them soak for 1 hour. After an hour, drain and rinse the cashews.
Place a large pot of salted water on the stove to boil, and cook pasta according to the package—reserve ½ cup of the pasta water for later use.
Heat a medium sauté pan over medium heat on the stove. Add the olive oil, and once heated, add the shallots and cook until they just start to brown, about 3 to 5 minutes. Next, add the garlic and cook until fragrant, about 30 to 60 seconds. Remove from heat and set aside.
Combine the browned garlic and shallots, soaked cashews, silken tofu, nutritional yeast, parmesan cheese, plant-based milk, lemon juice, lemon zest, salt, pepper, and red pepper flakes into a high-speed blender and blend until smooth, stopping to scrape down the sides as needed. Taste and adjust the seasoning for your preference.
Place the pasta pot back onto the stove over medium-low heat. Add the pasta sauce to the pot, along with the cooked pasta. Add the pasta water, a little at a time, and toss gently to combine. Add as much pasta water as needed to reach the desired consistency of the sauce.
Remove from heat, top with any of the optional toppings like chicken tofu, plant-based sausage, sauteed kale or spinach, extra parmesan, parsley, and lemon juice.
Storage Instructions: Store leftover Alfredo sauce in an airtight container in the refrigerator for 3 to 4 days; it may thicken as it chills, but it will loosen back into a silky consistency when warmed. This sauce also freezes beautifully for up to 2 months—simply thaw overnight in the refrigerator and blend briefly if it separates to restore its creamy smooth texture
Reheating Instructions: Reheat on the stovetop over low to medium heat, adding a splash of water or plant-based milk as needed to bring the sauce back to its original velvety consistency. If using the microwave, heat in 30-second intervals, stirring between each burst to keep everything smooth. From frozen, thaw completely in the fridge, then warm gently on the stovetop, blending or whisking lightly if the texture needs smoothing