How to Make It
In a food processor, finely chop the fennel and carrots. In a large saucepan, heat 1/3 cup of the olive oil. Add the onions, garlic, rosemary and the fennel mixture and cook over moderately low heat, stirring often, until the onions are very tender and starting to brown, about 25 minutes.
Add the crushed red pepper to the saucepan and cook over moderately low heat, stirring, for 1 minute. Add the chopped tomatoes and cook, stirring occasionally, until the sauce is thick, about 10 minutes; discard the rosemary sprigs.
Meanwhile, in a large pot of boiling salted water, cook the broccoli rabe until bright green, about 4 minutes. Drain and let cool, then coarsely chop.
In a large, deep skillet, heat the remaining 1/3 cup of olive oil. Add the broccoli rabe and cook over moderately high heat, stirring occasionally, until starting to brown, about 4 minutes. Add the tomato sauce and simmer over low heat until very thick, about 15 minutes. Season with salt. Transfer the broccoli rabe to a bowl and serve.