1 egg, 100g flour
Make a small mountain with your (strong) plain flour. Hollow out a crater. Crack your egg into the flour and using a chopstick or similar, start to beat the egg. Gradually add in the flour and keep mixing until a soft batter turns into a dough. Using your fingers, keep mixing and kneading the dough until it forms an elastic, non-sticky dough. Rest in a cold place for about 30 minutes.
Either using a pasta rolloer or a simple rolling pin, work the dough into as thin a sheet of pasta as possible. Add flour to keep the dough dry but workable. Either cut within a machine or roll pasta sheets up and slice to make into tagliatelle. Or sandwich one sheet on top of another with a filling.
Dry the pasta for at least an hour before cooking in boiling water for no more than 3 minutes.