Saute the onion in olive oil in a skillet over medium heat until translucent and starting to caramelize, 5-10 minutes.
Add the garlic, red pepper flake and tomato paste to the skillet, stirring to break up the tomato paste. Saute for 1-2 minutes, or until fragrant. Add the vodka, stirring a few times to coat and allow it to cook down (this happens rapidly).
Mix in the salt and tomatoes. Bring to a boil and let simmer uncovered until the sauce is very thick, about 15 minutes.
Meanwhile, cook linguine according to package directions until al dente.
Drain clams, reserving the clam juice.
Mix clams, heavy cream, and 1 tablespoon clam juice into the tomatoes. Add more clam juice to reach your desired consistency.
Toss cooked linguine with the sauce. Serve topped with shredded parmesan to taste.
Recipe by Alison's Allspice at https://www.alisonsallspice.com/clam-linguine-alla-vodka/