Pickled onions are delicious because the pickling process enhances their flavor by adding a tangy and slightly sour taste. Additionally, pickling onions helps to preserve them, making them a popular choice for many dishes.
Thinly slice the onions (I find a mandolin helpful!), and divide the onions between 2 mason jars or 2 airtight jars. Additional optional flavors: Place the garlic and peppercorns in each jar.
Heat the vinegar, water, sugar, and salt in a medium saucepan over medium heat. Stir until the sugar and salt dissolve, about 1 minute. Let cool and pour over the onions. Set aside to cool to room temperature, then store the onions in the fridge.
The pickled onions will be ready to eat once they're bright pink and tender - about 1 hour for very thinly sliced onions, or overnight for thicker sliced onions. They will keep in the fridge for up to 2 weeks. Enjoy over meats or in sandwiches!