smooth, about 3 minutes. Wrap in plastic. Let stand 15 minutes. For filling: Blend next 7 ingredients in processor. Set mixture aside. To assemble: Cut dough into 6 pieces. Flatten 1 piece of dough (keep remainder covered to prevent drying), then fold into thirds. Turn pasta machine to widest setting and run dough through. Repeat until dough is smooth and velvety, folding before each run and dusting with flour if sticky. Adjust pasta machine to next narrower setting. Run dough through without folding. Repeat, narrowing rollers after each run until pasta is about 0 cm thick, dusting with flour if sticky. Repeat with another piece of dough. Lay 1 dough sheet on lightly floured surface. Mound level teaspoons of filling at 5 cm intervals, leaving 1 cm border along edges. Brush dough between filling and along edges with water. Top with second sheet, pressing around filling to seal. Trim around filling using pastry cutter to create ravioli. Arrange ravioli on lightly floured waxed paper. Repeat with remaining dough. Let ravioli dry until leathery around edges. (Can be prepared 1 day ahead and refrigerated.) Stir 2 tablespoons olive oil into large pot of boiling salted water. Add ravioli (in batches if necessary) and cook until just tender but firm to bite, about 8 minutes. Drain well. Transfer to bowl. Add butter and toss well. Divide among 8 plates. Sprinkle each with freshly grated Parmesan cheese if desired. Top with freshly ground pepper.