Cook the pasta in boiling salted water until al dente, according to the package instructions.
Meanwhile, put the pancetta in a dry frying pan large enough to hold the pasta when cooked. Cook for 5 minutes until cooked through and lightly colored on the outside, then add the garlic and cook for 1 minute until soft but not colored. 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 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.
HOW TO MAKE SILKY PASTA SAUCES
Whenever you make a creamy pasta dish, always stir in a little of the pasta water to make the sauce silky smooth.