Instructions

For the filling: Pat beef dry with paper towels and season with salt and pepper. Melt butter in Dutch oven over medium- high heat. Brown beef on all sides, 7 to 10 minutes; transfer to plate.
Add cabbage and onion to fat left in pot and cook over medium heat until softened, about 3 minutes. Stir in garlic and rosemary and cook until fragrant, about 30 seconds. Stir in wine, scraping up any browned bits, then stir in broth. Return beef and any accumulated juices to pot and bring to simmer. Reduce heat to medium-low, cover, and simmer until beef is tender, about 1 hour.
Drain beef mixture in fine-mesh strainer set over bowl. Reserve ¼ cup cooking liquid; discard remaining liquid. Transfer beef mixture and liquid to food processor; process until finely ground, about 1 minute, scraping down sides of bowl as needed. Add Grana Padano, egg, and nutmeg and process until combined, about 30 seconds. Transfer filling to bowl; refrigerate for 30 minutes. (Filling can be refrigerated for up to 24 hours; bring to room temperature before proceeding with recipe.)
For the pasta and sauce: Transfer dough to clean counter, divide into 5 pieces, and cover with plastic wrap. Flatten 1 piece of dough into ½-inch-thick disk. Using pasta machine with rollers set to widest position, feed dough through rollers twice. Bring tapered ends of dough toward middle and press to seal. Feed dough seam side first through rollers again. Repeat feeding dough tapered end first through rollers set at widest position, without folding, until dough is smooth and barely tacky. (If dough sticks to fingers or rollers, lightly dust with flour and roll again.)
Narrow rollers to next setting and feed dough through rollers twice. Continue to progressively narrow rollers, feeding dough through each setting twice, until dough is very thin and semi-transparent. (If dough becomes too long to manage, halve crosswise.) Transfer sheet of pasta to liberally floured sheet of parchment paper. Cover with second sheet of parchment, followed by damp kitchen towel, to keep pasta from drying out. Repeat rolling with remaining 4 pieces of dough, stacking pasta sheets between floured layers of parchment.
Liberally dust 2 rimmed baking sheets with flour. Transfer filling to 1-gallon zipper- lock bag. Snip off 1 corner of bag to create ¾-inch opening. Position 1 pasta sheet on lightly floured counter with long side parallel to counter edge (keep remaining sheets covered). Using pizza cutter or sharp knife, trim pasta into uniform 4-inch-wide sheet. Pipe filling lengthwise down center of sheet, leaving 1-inch border at each end. Lightly brush edges with water. Fold bottom edge of pasta over filling until flush with top edge. Gently press to seal long edge of pasta flush to filling; leave narrow edges unsealed. With index finger and thumb of both your hands facing downward, pinch filled portion of pasta together at 1-inch increments to create individual sections.
Using fluted pastry wheel or pizza cutter, trim excess dough from filled pasta strip, leaving ¼-inch border on ends and 1-inch border on top. Starting at bottom edge of strip, roll pastry wheel away from you in one motion between pinched sections to fold and seal dough and separate agnolotti. Pinch edges of each agnolotto to reinforce seal, then transfer to prepared sheets. Repeat with filling and shaping remaining pasta sheets (you should have about 75 agnolotti). Let agnolotti sit uncovered until dry to touch and slightly stiffened, about 30 minutes. (Agnolotti can be wrapped with plastic and refrigerated for up to 4 hours or chilled in freezer until firm, then transferred to zipper-lock bag and frozen for up to 1 month. If frozen, do not thaw before cooking; increase simmering time to 4 to 5 minutes.)
Cook butter, hazelnuts, and ¼ teaspoon salt in 12-inch skillet over medium- high heat, swirling skillet constantly, until butter is melted, has golden-brown color, and releases nutty aroma, about 3 minutes. Off heat, stir in vinegar; set aside. Bring 4 quarts water to boil in large pot. Add half of agnolotti and 1 tablespoon salt and simmer gently, stirring often, until edges of pasta are al dente, 3 to 4 minutes. Using slotted spoon, transfer agnolotti to skillet, gently toss to coat, and cover. Return cooking water to boil and repeat cooking remaining agnolotti; transfer to skillet. Add 2 tablespoons cooking water and gently toss to coat. Sprinkle with parsley and serve immediately.