Fold dough into thirds, creating another rectangle; feed open edge through roller set at widest setting. Fold again; roll twice more using the same setting. Decrease setting one notch and roll pasta through again; repeat, decreasing setting by one notch each time until you’ve reached the second-to-last setting, creating a 1/16”-thick sheet.
Unroll strips and toss with flour; spread on a floured parchment sheet. Let dry for 30 minutes. To serve: Cook tagliatelle in salted boiling water until al dente, 3-4 minutes. Drain, transfer to a bowl and toss with 2 cups ragù. Serve with grated parmigiano-reggiano. Serves 4.