1Soak cashews in boiling water for 15 minutes, then drain.
2Melt vegan butter over medium heat, add garlic, and sauté until golden and fragrant.
3Combine soaked cashews, oat milk, nutritional yeast, lemon juice, apple cider vinegar, salt, and the sautéed garlic butter in a high-speed blender and blend until silky smooth.
4Pour the mixture back into the pan over low heat and stir until it thickens.
5Toss in the cooked fettuccine with the starchy pasta water to combine.