
Sauté the aromatics. In a large pot set over medium heat, warm the olive oil. Add the onion, carrot, and fennel and cook, stirring occasionally until softened and beginning to slightly brown, about 10 minutes.
Caramelize the tomato paste. Add the tomato paste and cook, stirring, until it darkens in color and begins sticking to the bottom of the pot, about another 2 to 3 minutes. Add the garlic and red pepper flakes and cook just until fragrant, about a minute.
Deglaze with wine. Pour in the white wine and stir, picking up any stuck bits. Simmer until the wine has evaporated.
Simmer the sauce. Add the vegetable broth, canned tomatoes, lentils, and salt. Bring to a boil, reduce heat and simmer, partially covered, until the lentils are tender and falling apart, about 30 minutes. Meanwhile, cook pasta according to package directions, if you like.
Blend for texture. Use an immersion blender to blend the sauce until it is thick and a bit chunky — you don’t want it perfectly smooth. Season to taste with additional salt. Serve over cooked pasta.