I start by slicing the red onions as thin as possible. A mandoline works best here because the thinner the slices, the faster they soak up the flavors.
Next, I combine apple cider vinegar, honey, water, salt, and chili flakes in a small saucepan. I let it simmer gently for about two minutes until the honey dissolves completely.
I place the sliced onions into a clean glass jar, then pour the hot brine over them. I make sure every slice is submerged so they pickle evenly.
I let the jar sit at room temperature for about an hour. This step lets the onions soak up the flavors without being too hot to handle.
Once cooled, I seal the jar tightly and refrigerate it. While they’re technically ready after two hours, I find overnight chilling really enhances the flavor.
When I’m ready to eat, I use a fork to transfer the bright pink onions onto tacos, sandwiches, or salads. They instantly add a sweet-spicy kick and a splash of color.