In a medium saucepan set over low heat, combine the oil, rosemary sprigs, sliced garlic, and red pepper flakes. Heat for 3-4 minutes.
Using a vegetable peeler, cut the peel from the orange. Slice the peel into thin strips. Set aside. Cut the white pith off of the orange and discard. Cut the orange crosswise into round slices and set aside.
Add the olives and the sliced orange peel to the oil mixture. Heat until warmed through, about 2-3 minutes. Remove the pan from the heat and allow the olives to cool and marinate for 30-45 minutes.
Transfer the olive mixture to a glass jar and store in the refrigerator for up to 7 days. Bring the olives to room temperature before serving.
Notes
Save the remaining orange slices for snacking.
Serve these olives with cheese boards or antipasto platters. Add to salads, brunch buffets, or appetizer spreads. Gift small jars to friends and family during the holidays.