-- From "Mexico One Plate at a Time" by Rick Bayless. Onions may be made several days ahead of time and refrigerated until ready to use.
- Combine lime and orange juices in a small bowl and set aside.
- Place the onions in a non-aluminum bowl. Pour boiling water over them and wait 10 seconds, then pour the onions into a strainer.
- Return the drained onions to the bowl, pour on the citrus juices and stir in salt. Cover and set aside until serving time. Just before serving, drain onions and set out in serving bowl.