01 - Pack sliced red onions into a clean 2-cup heatproof jar. Layer garlic cloves, red pepper flakes, and peppercorns throughout the onions.
02 - Combine apple cider vinegar, water, hot honey, sugar, and salt in a small saucepan. Bring to a simmer over medium heat, stirring constantly until sugar and salt dissolve completely.
03 - Carefully pour hot brine over onions, ensuring they are completely submerged. Press down firmly with a spoon to release air pockets and fully immerse all vegetables.
04 - Allow mixture to cool to room temperature, approximately 30 minutes. Cover tightly and refrigerate for minimum 1 hour before serving. For optimal flavor development, marinate overnight.
05 - Keep refrigerated and use within 2 weeks for best quality. Always use clean utensils when removing onions from jar.