Place a large pot of water on the stove for pasta. Also put up a deep skillet for sauce and a nonstick skillet for shrimp.
Gather your ingredients.
Peel and finely chop the onion.
In a large deep skillet, heat EVOO, a turn of the pan. Add 2 tablespoons butter and when it foams add the onions. Stir to soften while you peel and chop the garlic. Add 2 cloves of chopped garlic to onions and season with salt. Stir in 1/2 teaspoon of chili paste or about 1/4 teaspoon of red pepper flakes. Add vodka and reduce by half, 2 to 3 minutes. Add tomatoes and tear in a few leaves of basil. Reduce heat and simmer sauce, 10 minutes.
Season pasta water with a fat tablespoon of salt, add penne and cook 1 minute less than package directions, about 8 minutes. Have a mug or measuring cup on hand.
Add shrimp to a medium bowl and toss with remaining garlic. Thinly slice a lemon and toss with shrimp.
In the second skillet, heat EVOO, 2 turns of the pan, over medium-high and melt in 2 tablespoons butter. Add the shrimp mixture and toss 2 to 3 minutes; shrimp should be pink and opaque. Add a splash of Pernod or vermouth, the remaining red pepper flakes, a little salt and parsley; toss. Turn off heat.
Add cream to sauce and stir. Add shrimp to sauce, bring back to a bubble and turn off heat.
Reserve about 1/2 cup of starchy salty water and drain pasta or transfer to sauce with a spider. Toss pasta with sauce and grated cheese, using water to loosen as necessary.
Transfer pasta to large serving bowl or to individual shallow bowls to serve.