Step 1

Fill a 4- to 5-quart pot with water and bring to a boil over high heat. Add half of the onion, half of the celery and 2 teaspoons of the salt, and cook for about 1 minute. Stir in the lentils and return the water to a boil. Reduce the heat so the liquid is simmering and cook, uncovered, stirring once or twice, until the lentils are almost tender, 20 to 25 minutes.

Step 2

Meanwhile, in a medium (10-inch) skillet over medium heat, combine the oil and pancetta. Once the pancetta starts sizzling and has rendered a little of its fat, add the remaining onion and celery, along with the carrot, garlic and parsley. Cook, stirring often, until the vegetables are tender, about 8 minutes.

Step 3

Add the tomato puree, tomato paste, the remaining 1/2 teaspoon of salt and the crushed red pepper flakes, and mix well. Reduce the heat to medium-low and cook, stirring frequently, for 10 minutes.

Step 4

When the lentils are tender, transfer the pancetta-tomato mixture to the pot with the lentils (with the cooking water in it), and stir to incorporate. Reduce the heat to medium and cook for 10 minutes, stirring occasionally.

Step 5

Add the pasta, increase the heat to medium-high, and bring the mixture to a boil. Cook, stirring frequently so nothing sticks to the bottom of the pot, at least 5 minutes, depending on the type of pasta used. The pasta can be firm or soft, and the dish can be soupy or dry; it's up to you. Add water as needed, a little at a time, to keep the mixture boiling and until it reaches the desired consistency.

Step 6

Remove from the heat and let stand for 5 minutes. Divide among individual shallow bowls, drizzle with more oil and serve right away.