Here is how I made it:

Lemon-Lime Marmalade

2 1/2 cups chopped lemon pulp

2 1/2 cups chopped lime pulp

1 cup thinly sliced lemon peel

1 cup thinly sliced lime peel

1 1/2 quarts water

1 package pectin

sugar

Combine all ingredients except the pectin and sugar in a large pot.  Bring to a boil then simmer 5 minutes.  Let sit, covered, for 12 hours.  Measure the lemon-lime mixture then return to the pot.  Add pectin and bring to a boil.  Add sugar–cup per cup for what the lemon-lime mixture measured–and stir to dissolve.  Bring to a rolling boil.  Boil hard one minute.  Put in jars, leaving 1/4-inch headspace.  BWB 10 minutes.

Warning:  this is sweet and TART!  I actually added an extra cup of sugar and it's still very TART!  But good!  I like it, but this might not be for everyone.  It's definitely different!  I wouldn't sit around eating it straight with a spoon, though, LOL.  It's something that will be good cut by being added to something else in a recipe, on toast maybe with some cream cheese (to help cut it) etc.

And it made a ton.  I made 4 pints and 5 half-pints.

Thumbprint cookies?  I'll bet it'd be good in them!  Possibly with a
slightly sweeter than normal cookie part… the sweet/tart combo would be
extra good on a hot summer day.