Place the flour on a clean work surface and make a well in the centre. Crack the eggs into the well. Using a fork, gently beat the eggs, slowly incorporating the flour from the edges. When the dough comes together, knead by hand for 8–10 minutes until smooth and elastic. Shape into a ball.

Divide the dough into 2–3 pieces. Roll out each piece with a rolling pin (or pasta machine) into thin sheets, about 1 mm thick. Lightly dust with flour, fold the sheets, and cut into tagliatelle about 7–8 mm wide. Arrange the pasta on a floured surface or tray.

Place the guanciale in a cold pan and cook over medium-low heat until the fat renders and the guanciale becomes translucent, about 5–7 minutes. Add the sliced onion and cook gently in the rendered fat until soft and lightly golden, about 8–10 minutes. Add the tomato pulp and passata, stir well, and simmer over low heat for 15–20 minutes, until the sauce thickens and the flavours come together.

Bring a large pot of salted water to a rolling boil. Cook the fresh tagliatelle for 2–3 minutes, until tender. Drain the pasta, reserving a little cooking water. Add the pasta to the sauce and toss gently, adding a splash of pasta water if needed to bind the sauce.