Step 1

In a large pot, combine the carrot, the sliced onion, celery, fennel seeds, broth and 2 cups water. Bring to a boil over medium-high, then cover, reduce to medium-low and simmer until the vegetables have softened, 10 to 12 minutes.

Step 2

Remove the pot from the heat and, using a slotted spoon, transfer the solids to a blender, draining off as much liquid as possible. Add 1 cup of the broth to the blender along with the still-frozen peas and the parsley; leave the remaining broth in the pot so it remains warm. Blend until the mixture is smooth, 1½ to 2 minutes; you should have about 3 cups puree. Set aside in the blender jar.

Step 3

In a large saucepan over medium, combine the chopped onion, pancetta and 2 tablespoons butter. Cook, stirring occasionally, until the onion is lightly browned and the pancetta is rendered and lightly browned, 6 to 8 minutes.Add the rice and stir until the grains are coated with fat, then stir in 1 cup of the broth. Cook, stirring, until the liquid is mostly absorbed, about 5 minutes. Ladle in additional broth to barely cover the rice and simmer, stirring often, until the broth is mostly absorbed.Repeat the addition of broth and simmering until mostly absorbed 4 or 5 times, until the rice is al dente and most of the broth has been used; this process should take 25 to 30 minutes.

Step 4

Remove the pan from the heat and let stand uncovered for 5 minutes. Add the thawed peas and the puree, then stir until heated through, about 1 minute. Add the remaining 2 tablespoons butter and stir until melted. Stir in the Parmesan, then taste and season with salt and pepper. Serve sprinkled with additional Parmesan.