Quick soak cashews: Add cashews and boiling water to a small heatproof bowl. Let soak (for at least 10 minutes) while you cook (see note 4).
⅓ cup raw cashews, 1⅓ cup boiling water
Boil water for pasta: Bring a large pot of salted water to boil.
Start sauce: Meanwhile, warm olive oil in a large pot over medium heat. Add onions, cook until golden around the edges, about 6 minutes. Add garlic and red pepper flakes, cook until fragrant, 1 to 2 minutes. Add tomato paste and cook, stirring frequently, until it's dark red and sticking to the bottom of the pot, 8 to 10 minutes. (If the tomato paste sticks as soon as you add it, reduce the heat slightly and continue cooking until the olive oil turns red).
3 tablespoons extra-virgin olive oil, 1½ cups diced yellow onion, 5 cloves garlic, thinly sliced, ¼ teaspoon red pepper flakes, 1 (5.3 oz/150g) tube tomato paste
Cook pasta: Meanwhile, cook pasta until al dente, according to package instructions. Scoop out 2 cups of the pasta water and set aside, then drain noodles.
1 lb dried penne
Finish sauce: Pour vodka over the tomato paste mixture. Cook until the liquid evaporates, about 1 minute, while scraping up anything stuck to the bottom of the pot. Transfer mixture to a high-speed blender, along with cashews AND soaking water. Blend until completely smooth and creamy.
¼ cup vodka
Combine: Pour the sauce back into the pot. Add salt and ¾ cup of the reserved pasta water. Warm over medium-low heat until bubbling, then add noodles and parmesan. Toss to coat. Add small splashes of more pasta water until noodles are coated in a luscious sauce. Taste and season with more salt if needed. Garnish with more parmesan and serve.
1 teaspoon fine sea salt, ⅓ cup grated vegan Parmesan