Sourdough Burger with Quick Pickled Onions

Method

1. In a small bowl, combine vinegar, sugar, salt, pepper, and red pepper flakes.
2. Add thinly sliced onions to the mixture and let sit for 15 minutes.
3. Cook the ground beef to desired doneness, about 5-7 minutes.
4. Toast the sourdough bun halves.
5. Assemble the burger with beef, pickled onions, lettuce, tomato, mayo, and mustard.
6. Check that the ground meat reaches 71°C (160°F) throughout before serving.