Cook the pasta in boiling salted water until al dente, according to packet instructions.
Meanwhile, put the pancetta lardons in a dry frying pan large enough to hold the pasta when cooked. Fry for 5 minutes until the lardons are cooked through and lightly coloured on the outside, then add the garlic and cook for 1 minute until soft but not coloured. Turn off the heat.
Three minutes before the pasta is ready, add the peas to it to cook through. Drain well, reserving a couple of tablespoons of the cooking water.
Tip the pasta and peas into the pan with the pancetta and stir well over a low heat. Add the crème fraîche and stir until melted, adding a tablespoon or two of the pasta cooking water to loosen if necessary. Dot in the ricotta, gently mixing. Taste and adjust the seasoning as necessary.
Serve the farfalle hot, drizzled with a little olive oil.