Preheat oven to 425°F. Drizzle garlic bulb with olive oil and season with salt and pepper. Wrap in foil pouch and roast until tender, about 40 minutes. Remove and cool.
Char peppers under broiler with oven door ajar to let steam to escape. When blackened evenly all over, remove and cool in a covered dish or bowl to handle. Peel and seed peppers.
Bring a large pot of water to a boil for the pasta.
Toast nuts in a small pan over medium heat until fragrant and toasted.
Place peppers in food processor with half the nuts. Squish garlic from skins and add to processor with half a cup of cheese, salt, pepper, basil, parsley, citrus zest and chili flakes. Pulse chop then stream in about 1/4 cup good EVOO to form pesto. Taste to adjust seasoning.
Salt pasta water and cook pasta to
al dente. Reserve 1 cup starchy liquid then drain pasta.
In a warm serving bowl, combine mascarpone, crème fraiche or cream with half the starchy water and the pesto. Add pasta and toss and coat, using remaining water as needed to cover the pasta with sauce evenly. Serve topped with remaining toasted and cheese at the table.