Place the flour in a bowl and add 2 of the eggs. Use your hands to combine the flour and eggs to create dough. Knead for about 5 minutes until the dough has all come together, then wrap in cling film and place in the fridge to rest for 30 minutes.
Meanwhile, beat the ricotta, lemon zest, thyme leaves and ½ teaspoon of the truffle salt together with a wooden spoon. Taste and add a little more salt if necessary. Set aside.
Cut the dough in half and start winding it through a pasta machine on the largest setting. Dust with a little flour, fold and pass through again. Repeat this process for 5 – 10 minutes until your dough is very smooth and elastic, then start to run through on smaller and smaller settings until you have a very long, shiny piece of pasta dough at the thinnest setting. Brush with a little flour and set aside, repeating the whole process with the second half of the dough.
Lay one of the sheets of pasta on a well-floured surface and place four mounds of the ricotta mixture onto the pasta sheet, spaced well apart. Make a well in the centre of each mound.
With the remaining four eggs, separate each egg yolk from the whites, carefully placing one yolk into each well and sprinkling with a small pinch of truffle salt. Brush around the ricotta with a little water or lightly beaten egg white, then cover with the other sheet of pasta and use your fingers to seal around the ricotta, making sure no air is left inside. Cut around each ravioli with a knife or pasta cutter.
Bring a large saucepan of well-salted water to a rolling boil and cook the ravioli for about 2 minutes, then remove and drain. Place onto warm plates.
Meanwhile, dice the butter and place in a frying pan to melt. Cook over medium heat until nutty and brown, then add the sage and fry until crisp. Quickly add the lemon juice, stir to combine, then spoon over the ravioli.
