1. Prepare canner, jars, and lids.
2. Using a vegetable peeler, remove the zest (the yellow part of the peel) from the lemons in strips. Cut strips into thin slices.
3. Using a sharp knife, cut the white pith from lemons, exposing the juicy parts of the segments. Working over a large bowl to catch juice, cut the lemon segments from membrane. Place segments in bowl and squeeze membrane to remove as much juice as possible, collecting in bowl. Fish out any seeds that fell into the bowl and discard them along with the membrane.
4. Peel and grate the ginger if you haven’t done so already.
5. In a large deep stainless steel saucepan, combine lemon peel, baking soda, and water. Bring to a boil over high heat. Reduce heat and boil gently for 5 minutes until peel is softened. Remove from heat and set aside.
6. Measure 1 cup lemon segments and juice. Add to the pan with the lemon peel along with the ginger. Whisk in pectin until dissolved.
7. Bring to a boil over high heat, stirring constantly. Add sugar all at once and return to a full rolling boil, stirring constantly. Boil hard, stirring constantly, for 1 minute. Remove from heat and skim off foam.
8. Ladle hot marmalade into hot jars, leaving 1/4-inch headspace. Remove air bubbles and adjust head space if necessary by adding hot marmalade. Wipe rim. Center lid on jar. Screw band down until resistance is met, then increase to fingertip-tight.
9. Place jars in canner, ensuring they are covered by at least an inch of water. Bring to a boil and process for 10 minutes. Remove lid from the pot. Let the jars sit in the pot for 5 minutes, then remove jars, cool, decorate the jars so they’re super-cute and give them away to deserving friends and family members.