Bring a large pot of salted water to a boil for the pasta. In a cold Dutch oven or heavy-bottomed skillet, combine the olive oil, diced onion, diced fennel, and minced garlic. Set over medium-low heat and sauté for about 15 minutes, stirring occasionally, until the vegetables are soft and translucent but not browned.

Stir in the Calabrian chili paste (or red pepper flakes) and season with salt. Cook for 1-2 minutes on medium-low until fragrant. Add the tomato paste and honey, stir to incorporate, and continue cooking over medium heat for 4-5 minutes, stirring frequently, until the tomato paste starts to caramelize and the oil turns bright red. Stir in the white vinegar, then turn off the heat. The sauce should taste slightly more pungent than desired, as it will be mellowed by the pasta.

Cook the pasta in the boiling water according to package instructions until just barely al dente. Reserve ¾ cup of pasta water before draining. Transfer the cooked pasta to the skillet with the sauce using a slotted spoon and stir to combine.

Set the Dutch oven over medium heat and cook for 1-2 minutes, adding pasta water a little at a time to loosen the sauce to your desired consistency. The sauce should cling to the pasta while remaining saucy. Adjust seasoning with salt and add more chili paste if desired. Serve immediately, garnished with grated Parmigiano-Reggiano cheese.