Step 1

Prepare waterbath canner, 6 half pint jars & lids, keeping warm until needed.

Step 2

Cut ends off onions and peel; slice in half and cut each in half again, lengthwise (or in thirds if onions are big). Turn halves and cut into 1/4 inch slices widthwise (as pictured in tutorial). Place slices in an 8 quart measuring cup - you should have 6 cups of onion slices.

Step 3

Add prepared onions, apple juice, vinegar, garlic, salt, pepper, mustard and red pepper flakes to an 8 quart stockpot. Gradually stir in pectin and then add butter if using. Bring to a boil that can't be stirred down over high heat, stirring constantly.

Step 4

Add honey and sugar; return to a full boil and let boil for 1 minute, stirring constantly. Remove from heat (skim foam if needed).

Step 5

Ladle hot marmalade into prepared half pint jars one at a time, leaving 1/4-inch headspace. Wipe rims, attach lids, and place in canner.

Step 6

Place lid on canner and bring to a gentle, steady boil - process for 10 minutes, maintaining steady boil the entire time. Turn off heat, and let jars cool in canner 5 minutes before removing jars to a towel lined surface to cool for 24 hours. Check lids for seal before labeling and storing in a cool, dark place (with rings removed).