Heat the oven to 350° F. Spread the walnuts on a small baking sheet and bake for 5 to 7 minutes, until they have turned a shade darker and are fragrant. Let them sit until cool enough to handle, then rub off as much of the thin skins as possible.

Transfer the walnuts to a marble mortar and pound to a coarse paste with the garlic. Add the basil and marjoram leaves and drizzle in the oil. Pound and stir with the pestle until thoroughly combined. Sprinkle in the sea salt and a few grindings of white pepper and stir well. Add the ricotta to the mortar by the spoonful, stirring to incorporate it with the other ingredients. Once you have added all the ricotta, give the pesto a vigorous stir to make it light and fluffy. Taste and add more salt and pepper if necessary.

If using a food processor or blender, blitz the nuts to grind them up. Add the garlic, herbs, oil, salt and pepper and process or blend again. Add the ricotta and process/blend briefly to incorporate the ingredients. Transfer to a bowl and stir vigorously to incorporate air and make the pesto fluffy.

If not using immediately, spoon the pesto into a container with an air-tight lid and refrigerate. Otherwise, if you're going to use the pesto as a sauce for pasta, transfer it to a bowl and stir in 3 or 4 tablespoons of whole milk to loosen it.

To make pasta with white pesto, bring a pot of water to a rolling boil and salt it generously. Cook the pasta (I used a shape called 'rocchetti' which is, essentially, large cavatelli) until al dente. Drain, reserving a little of the cooking water, and return the pasta to the pot. Spoon the pesto into the pasta (you might not use all the pesto) and stir to incorporate it. Stir in the Parmigiano and add a splash or two of the pasta water to loosen the sauce if necessary. Spoon into bowls and serve with more Parmigiano for sprinkling on top.