Peel and de-vain the shrimp and save any shells or tails you peeled. If your shrimp doesn’t have the shells on, you can just use the tail.
Take the shrimp and slice it into 3 smaller pieces, one cut in half to separate the narrower end of the shrimp. Then stand up the thicker end, and slice that down the middle to give you about 3 equal-sized pieces.
Slice the garlic thin and finely dice the parsley.
Get a pot of salted water boiling, a pot not too big relative to the pasta. We want a low enough level of water to concentrate the starches that release into the water, so if using a large pot, don’t feel like you need to fill the entire pot up with water.
In a large saute pan, add a tablespoon or two of olive oil to the pan and get it hot on medium-high heat. Once hot, add the shrimp shells and toast them for a few minutes to pull out that shrimp flavor. Then add the wine and lower the heat to a simmer, we don’t want the wine to reduce too much, just to infuse with the shrimp shell flavor. After about 5 minutes of simmering, strain out the wine and set aside.
Once the water is boiling add the pasta. The Rigati takes 12 minutes to make, so I let the pasta cook for the first 6 minutes and then make the sauce in the final 6 minutes. After 5 minutes, I get the heat on medium-high heat and add a knob of butter and a tablespoon of olive oil. Once hot, add the garlic and chili flake and cook for about 2-3 minutes and then add the shrimp-infused wine you made earlier the lemon juice, and bring it to a simmer.
Now there should be about 3 minutes left of cooking, add the shrimp and gently simmer and poach the shrimp on medium-low heat, stirring it every now and then. Two minutes before the pasta is perfectly cooked, use a Spyder and fish out the pasta, and transfer to the sauce. Now you can kick up the heat to high, add a tablespoon or two of pasta water at a time and as needed, tossing and stirring the pasta and to try and thicken the sauce. Pasta will absorb some of the sauce, and the starch in the pasta, and the heat will gradually reduce and thicken the sauce. Once that pasta is al dente, sprinkle in a handful of the diced parsley and start to slowly toss and stir in cold butter. This will also aid in thickening the sauce. Add the butter in batches, slowly working it into the sauce and then once the sauce is thick but still flowing, kill the heat and serve. As the sauce cools, it will continue to thicken. Taste and adjust the seasoning.