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1
Place a small plate in the freezer so you can test the jam for proper thickness later. Make sure your jars and lids are sterilized and ready to go.
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2
Use a zester to remove the zest from the Mandarin oranges. Add the zest to a large, deep, heavy-bottomed pot. Remove the remaining peels from the oranges. Wrap the peels in cheesecloth, along with the lemon verbena leaves, and secure with butcher's twine. Add to the pot alongside the zest.
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3
Remove seeds from oranges, then pulse the orange flesh in a food processor to chop the segments into coarse chunks that are about 1/4-inch across, 4 to 5 short pulses. Add the oranges to the pot with the zest and peels.
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4
Add orange juice, lemon juice, and water to the pot and bring to a boil over medium heat. Once boiling, lower heat to low and simmer for 20 minutes. Remove from heat and allow to cool. Once cool, remove the bag of peels from the pot and gently squeeze the juice from the bag. Do not wring it completely, which will make the marmalade overly bitter-just release any loose, excess juice absorbed by the peels and then discard the bag.
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5
Add Campari, sugar, butter, and salt to the pot, stirring well to combine. Cook over medium heat, stirring frequently, until the fruit begins to bubble and spit. Reduce heat to a bare simmer and cook for 30 minutes longer, stirring frequently to keep the fruit from burning.
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6
Begin testing the marmalade for doneness: Spread 1/2 teaspoon of cooked fruit on the cold plate and place it back in the freezer. Wait 30 seconds, then run your finger through the fruit. It should be thick enough to maintain a path when you run your finger through it. If you'd like thicker marmalade, place the plate back in the freezer and cook the fruit for another 4 minutes and test again. Repeat until desired thickness is achieved, but be careful about cooking too long or you will alter the taste of your marmalade.
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7
Remove pot from heat and use a spoon to skim any foam from the surface of the fruit. Ladle marmalade into sterilized jars and process them in a hot water bath for 10 minutes. Unopened jars will keep at room temperature for up to 6 months. Opened marmalade should be refrigerated.
