Bring a large pot of water to a boil and add the tagliatelle. Cook according to the packet instructions, until the pasta is al dente.
Meanwhile, heat up a frying pan to medium-high heat. Add the pancetta to the pan and fry it until it is beginning to turn golden.
Add the butter, the mushrooms, and the garlic paste to the pan and fry for a few minutes until the mushrooms are softening.
Add the cream to the pan and mix with the pan's juices. Once the cream is warmed, add the grated Parmesan and the black pepper, and stir them in until a smooth sauce has formed.
Drain the pasta, reserving 1 cup of pasta water, and then add the pasta to the pancetta and mushroom sauce. Mix everything together before serving, adding enough of the pasta water to create a silky sauce that sticks to the tagliatelle. Serve topped with an extra sprinkling of Parmesan if desired.