1. Bring a large pot of lightly salted water to a boil. Add pipette and cook 8 minutes or according to package directions. Drain, reserving 1 cup of the pasta water.
2. Meanwhile, brown sausage in a large saute pan over medium-high heat, stirring occasionally, 5 to 7 minutes. Remove sausage to a plate with a slotted spoon.
3. Reduce heat to medium. Add oil to the same pan; stir in fennel and onion. Cook 10 to 12 minutes, until vegetables are softened. Pour in orange juice and zest, scraping bottom of pan to release any brown bits. Stir in sausage, pasta, 1/2 cup of the reserved pasta water (add remaining water 1/4 cup at a time if it seems dry), 1/2 cup of the Parmesan and the salt. Garnish with remaining 1/4 cup Parmesan and the reserved fennel fronds.