Cut cooled rind into long thin slivers, then coarsely chop to make a full cup.
Peel and remove pith from chilled oranges. Slice oranges in between membranes into segments or supremes.
Retain membrane dividers and place onto a square of cheesecloth to tie into a pectin bag.
In a wide, heavy-bottomed saucepan combine sugar, 1½ cups water, 1 cup cooking liquid from rind prep, slivered orange rind, orange segments and juice, pectin bag, chopped jalapeño and ½ teaspoon red pepper flakes.
Bring mixture to a rolling boil and maintain boil until mixture reaches 220° F. Be patient, this could take 45 minutes.
Test mixture to make sure it is gelling, using cold plates from the freezer.
When marmalade reaches desired consistency, turn off heat. Stir in 1/8 teaspoon red pepper flakes to taste and lemon zest.
Marmalade can be refrigerated up to 4 weeks or preserved using water bath canning process. Makes 5 ½-pint jars.
PRO TIP: The addition of red chili flakes at the end helps color the marmalade.