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1
Place the tomatoes in a large pot and pour the boiling water over the tomatoes; allow to sit 5 minutes. Remove tomatoes from boiling water and place in ice-cold water until cool enough to handle. Slip off skins and stems.
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2
Coarsely chop the tomatoes in a food processor; reserve any juices and add to chopped tomatoes.
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3
Combine vinegar, apple juice, brown sugar, salt, black pepper, mustard, allspice, cumin, and cayenne pepper in a large non-reactive pan over medium heat; cook and stir until sugar dissolves completely; stir in the chopped tomatoes. Bring the mixture to a boil; reduce heat and simmer, stirring frequently, until liquid has reduced by half, 30 to 45 minutes. Add the lemon slices and cook another 15 minutes.
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4
Sterilize the jars and lids in boiling water for at least 5 minutes. Pack the jam into the hot, sterilized jars, filling the jars to within 1/4 inch of the top. Run a knife or a thin spatula around the insides of the jars after they have been filled to remove any air bubbles. Wipe the rims of the jars with a moist paper towel to remove any food residue. Top with lids, and screw on rings.
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5
Place a rack in the bottom of a large stockpot and fill halfway with water. Bring to a boil over high heat, then carefully lower the jars into the pot using a holder. Leave a 2 inch space between the jars. Pour in more boiling water if necessary until the water level is at least 1 inch above the tops of the jars. Bring the water to a full boil, cover the pot, and process for 30 minutes.
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6
Remove the jars from the stockpot and place onto a cloth-covered or wood surface, several inches apart, until cool. Once cool, press the top of each lid with a finger, ensuring that the seal is tight (lid does not move up or down at all). Store in a cool, dark area.
