I first envisioned this recipe without the sausage, as a warm-your-bones vegetarian pasta option for the depths of winter. And it was very good. But adding a little sausage made it great—the brawny flavor of the meat giving the lentils a deep complexity that makes them even richer and a little creamier. This said, you can make this without the meat, though don’t stint on adding oil at the end to compensate for the loss of richness. Serve this with a sautéed, strongly flavored leafy green--kale, broccoli rabe, or even radicchio. And open a really nice bottle of red.