1small red onionhalved through root end, thinly sliced lengthwise (upright)
3sprigs rosemary
4Tbsp.extra-virgin olive oildivided, plus more for drizzling
Kosher salt & freshly ground pepperto taste
6sweet Italian sausagesabout 1 1/2 lb. total
1medium navel orange
1Tbsp.red wine vinegar
Flaky sea salt
Instructions
Place a rack in highest position in oven; preheat to 425°F. Combine fennel bulbs, red onion, and rosemary sprigs on a large rimmed baking sheet. Drizzle with 3 Tbsp. oil, season generously with kosher salt and pepper, and toss to combine. Arrange sausages on top, spacing evenly and nestling into vegetables. Prick sausages all over with the tip of a paring knife and drizzle with 1 Tbsp. oil. Roast until sausages are browned on top and cooked though and fennel is tender and deeply browned in spots, 25–30 minutes.
Meanwhile, coarsely chop reserved fennel fronds (you want about 1/4 cup); set aside. Cut the ends off orange to reveal flesh. Rest orange upright on a cut side and cut down around orange to remove peel and white pith, rotating it as you go; discard peel. Working over a small bowl, hold orange in your hand and cut between membranes to release segments into bowl. Squeeze membranes to extract any remaining juice into bowl; discard membranes. Add vinegar to orange segments and juice and toss to combine; season with kosher salt and pepper.
Remove baking sheet from oven. Using your hand or a spoon to block segments, pour juices from orange over sausage and fennel mixture. Set orange segments aside and let sausages and fennel mixture cool 5 minutes.
Transfer sausages and fennel mixture to a platter. Crumble rosemary leaves over and scatter reserved orange segments and fennel fronds on top. Season with sea salt and a bit more pepper; drizzle with oil.
Notes
a mandoline works great for slicing the fennel and onion.
Can use turkey Italian sausage, or other flavored pork or chicken sausage.
If desired, remove sausages and veggies after 30 minutes and place sausage on separate pan. Cover veggies with foil to keep warm. Broil sausages for a few minutes to finish browning. Then proceed with recipe.