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1
In a large soup pot or Dutch oven, heat 3 tablespoons of the olive oil over medium heat.
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2
Add onion, carrot and celery and cook, stirring occasionally, until golden brown, 12 to 15 minutes.
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3
Add tomato paste and cook, stirring constantly, for 1 minute.
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4
Add tomatoes one at a time, crushing them by hand, and adding any juice from the can.
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5
Season with salt and pepper to taste.
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6
Cover and reduce heat to low.
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7
Heat remaining 1 tablespoon olive oil in a large skillet over medium-high heat.
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8
Add beef, pork, veal and chicken livers, and season with salt and pepper to taste.
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9
Cook, breaking the pieces with a wooden spoon, until the meat is no longer pink, about 7 minutes.
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10
Using a slotted spoon, transfer the meat to the sauce.
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11
Add rosemary, sage, bay leaves and Parmigiano rind, if using.
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12
Cover, and simmer over low heat, stirring occasionally, for 1 1/2 to 2 hours.
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13
Discard rosemary, sage, bay leaves and cheese rind.
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14
Adjust salt and pepper to taste.
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15
Cook the pasta in a large pot of boiling, lightly salted water until al dente (about 2 minutes for fresh pasta, or follow manufacturers directions for dried), then drain well.
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16
Divide the pasta among four plates or bowls, and top with ragu.
