Scrub the blood oranges with a vegetable brush and hot water to remove any pesticides.

Cut off the tops and bottoms of the oranges to reveal the flesh. Quarter the fruit and remove any seeds.

Finely slice the orange quarters using a food processor, checking for any large pieces needing further chopping.

Transfer the sliced oranges to a nonreactive pot and add 1/2 cup of water. If there are larger pieces, return them to the food processor with the water to create a puree, then add to the pot.

Add enough water to cover the oranges, around another 1/2 cup. Bring to a boil, then remove from heat and cover. Let rest overnight.

The next day, bring the mixture to a boil again and let it sit overnight once more.

On the third day, measure the cooled mixture volume. It should be about 3 cups. Return to the pot, adding an equal amount of sugar and the remaining half cup of water.

Bring the mixture to a boil again, stirring constantly to prevent sugar from burning. Cook until reaching the gel stage, roughly 20-25 minutes.

After heating, let the marmalade rest for about 5 minutes, stirring gently to release trapped air.

Prepare a large pot of boiling water. Ladle the marmalade into clean, hot jars, leaving 1/4 inch of headspace. Wipe rims clean, center lids on jars, and screw on bands until fingertip-tight.

Process the jars in boiling water for 10 minutes. Remove and allow them to cool for 24 hours before checking seals.