1. Place the peppers in a dry, heavy-bottomed skillet set over high heat and roast, turning them as needed until they are blackened and charred all over. Remove the peppers to a heat-proof bowl and cover.
2. Let the peppers steam for 10 minutes.
3. When the peppers are cool enough to handle, remove the charred skin. Cut the peppers open and remove the seeds and stem. Roughly chop the skinned peppers and set them aside while you prepare the pesto.
4. Heat the olive oil in a large, heavy skillet. Add the red onion and sauté over medium-low heat until softened, but not browned. Add two to three Calabrian chili peppers and a teaspoon of the oil from the jar and stir to combine. Add the garlic and salt and sauté an additional minute until fragrant.
5. Add the tomatoes with their juices and the sugar and stir to combine. Raise the heat to high and bring the sauce to a boil. Then reduce the heat and simmer the sauce until thickened, about 10 minutes.
6. Purée the sauce using an immersion blender or transfer the sauce to a regular blender and purée it before returning it to the pan. Add the ricotta and grated Pecorino Romano to the pesto and stir to combine. Taste and adjust seasoning, adding more salt if necessary.
7. Store the pesto in the refrigerator until needed. Pesto Calabrese can be used as a sauce for pasta, as a topping for crostini or drizzle it on roasted vegetables. If serving it with pasta, cook the pasta according to package directions and then toss the warm pasta with the pesto Calabrese. Garnish with additional ricotta and fresh basil.