For the sweetest marmalade, go with red grapefruit. Pick fruit that feels slightly soft when squeezed (this indicates ripeness). Avoid fruit that feels light, as it may have too much peel and not enough juice. You’ll also need one traditional lemon (not Meyer lemon) for balance.

Since the peel is part of this recipe, rinse the grapefruit and lemon thoroughly under warm water, using your fingers to remove any debris. Avoid using a vegetable brush, as it may scratch the peel and ruin the texture.

Using a vegetable peeler, remove the grapefruit peel in long strips, avoiding the bitter white pith. Once you’ve mastered peeling the grapefruit, peel the lemon in the same way.

Now it’s time to chop your peel! If you're using this marmalade for spreading, finely chop the peel into small pieces. If you're using it as a glaze or marinade, you may want longer strips that can be removed later.

Combine the chopped peel with 1/8 teaspoon baking soda and 2 ½ cups water in a large stainless steel pan. Bring the mixture to a boil, then reduce the heat, cover, and simmer for 20 minutes, stirring occasionally.

While the rind simmers, sterilize your jars. Wash them in hot soapy water and inspect for cracks or chips. Any damaged jars should be set aside for non-canning purposes. Place the jars in the canner and cover with water, bringing it to a boil. Meanwhile, place the lids in a saucepan of water and simmer on low to soften the adhesive.

Cut the pith off the fruit with a sharp knife, then slice the grapefruit and lemon into sections. Over a bowl, slice through the membranes to release the juice and fruit. Discard the membranes and any seeds, then coarsely chop the fruit. Measure carefully to ensure you have exactly 2 ¼ cups of fruit and juice, as excess liquid can result in runny marmalade.

Add the prepared fruit and juice to the simmering rind mixture. Bring it to a boil. Once boiling, reduce the heat and let it simmer for 10 minutes, stirring regularly to prevent burning.

Stir in 6 tablespoons of powdered pectin all at once, then bring the mixture back to a rolling boil over high heat. A rolling boil means the marmalade will bubble vigorously and can't be stirred down.

Add all 4 cups of sugar at once, stirring constantly. Keep the heat high and the sugar should melt quickly. The marmalade should remain relatively clear. Bring it back to a rolling boil that can’t be stirred down, and let it boil hard for 1 minute while stirring continuously to avoid burning.

Using a jar lifter, remove the sterilized jars from the canner. With a canning funnel, fill the jars with hot marmalade, leaving about ¼ inch of space at the top. Marmalade is thick but should pour smoothly. If you notice any air bubbles, run a knife around the inside of the jar to release them.

Wipe the rims of each jar with a damp paper towel to remove any sticky residue. Using the lid lifter, place a lid on each jar and screw on a ring. Tighten the ring just enough to hold the lid in place—don’t over-tighten, as air needs to escape during canning.

Using the jar lifter, carefully place the filled jars in the water bath canner. Ensure the tops of the jars are covered with at least 1 inch of water. Bring the water to a boil and process the jars for 10 minutes. Be sure to adjust the time for your elevation if needed.

When processing is complete, turn off the heat and remove the canner lid. Let the jars sit in the water for 5 minutes to stabilize. After that, carefully remove the jars using the jar lifter and place them upright on a cutting board or towel to cool.

Leave the jars undisturbed for 24 hours. Afterward, check the seals by pressing on the center of each lid. If it’s depressed and doesn’t pop back, it’s sealed properly. If any lids aren’t sealed, refrigerate the jars and eat them within the next few days or freeze them.