- In a heavy-bottomed saucepan, melt butter over medium-low heat.
- Add the onions and fry until translucent, about 25 minutes.
- Add the vinegar, honey, salt, and pepper. Stir and cook, covered, about 30 minutes, stirring occasionally.
- Add apples and cook for another 30 minutes.
- Transfer confit into sterilized Mason jars, filling them 1 cm (1/2 inch) from the top. Seal and sterilize.
This recipe's acidity level means it can be canned using the boiling water technique.
- Sterilize jars by immersing in boiling water for about 5 minutes. The lids must be new to ensure a proper seal. Soak lids in hot water before using.
- Fill jars, leaving a headspace of about 1 cm (½ in.).
- Place lids and screw bands on jars but do not over-tighten.
- Immerse jars in boiling water and boil for at least 15 minutes.
- Remove jars from water and let rest for 24 hours. The lids will be depressed and make a sudden popping noise when the seal is tight.
- The jars can be stored for one year in a dark, dry, cool place.
This onion confit is delicious on burgers, meat paninis, in pasta, or served with grilled meat or cheese and crackers.