Grate the Parmesan, if using, and warm the serving plates.

Cook the pasta.

Bring plenty of water to the boil in a saucepan and add salt. Cook the tagliatelle according to the packet instructions. Keep the pasta slightly firm, as it will cook a little more in the pan. Before lifting out the pasta, set aside about 300 ml of the cooking water.

Make the truffle butter sauce.

Towards the end of the pasta's cooking time, melt the butter in a wide pan over a low heat. Don't let the butter brown. Grate a small amount of the truffle into the melted butter and let it warm through for a moment. Add about 100 ml of the hot pasta cooking water and stir. Save the rest of the truffle for finishing the plates.

Combine the pasta and sauce.

Lift the tagliatelle into the pan with tongs. Toss gently for about a minute. Add cooking water a little at a time until the sauce is glossy and coats the pasta evenly. The pasta should stay juicy.

Add Parmesan if you like.

Take the pan off the heat. If using Parmesan, add it finely grated and stir. Loosen with a splash of cooking water if needed. Taste before adding any salt.

Finish with fresh truffle and black pepper

Divide the pasta between warm plates and shave the truffle into thin slivers over each serving. Finish with black pepper. Serve immediately.