Orange-Tangelo Marmalade

I'm lucky enough to have both an orange tree and a lemon tree in my backyard, so even if I didn't love marmalade, I'd probably feel obligated to make it.  In the past I've used a recipe from Ball's Complete Book of Home Preserving, which calls for juicing the oranges and straining the juice through cheesecloth before slicing the orange peels.  While that recipe undoubtedly made some great-tasting marmalade, I wanted to try something simpler this year, so I modified this recipe from Alton Brown.  Slicing the oranges on a mandoline was quick (especially since my oranges are seedless), and the thin slices look pretty in the canning jars.  To cut the sweetness in the recipe a bit, I doubled the lemon juice, substituted a tangy tangelo for one of the oranges, and reduced the sugar by 6 oz.  This gave the marmalade just the right sweet/tart balance for me, though I recommend checking the marmalade for gelling before you reach 222 degrees, as mine has a firmer set than I would prefer.