Wash 2 or 3 of the oranges and zest them, carefully avoiding the white pith underneath. You should have about a tablespoon. Peel all of your fruit, removing as much of the pith and filaments as possible. Working over a bowl to catch the juices, cut each orange in half around its equator, and pick out any seeds. Place the halves along with any juice they've expelled in a food processor and process for about a minute, until you have a chunky purée.
Combine the orange purée, zest, sugar and lemon juice in a large, heavy saucepan. Bring to a boil over medium-high heat, then reduce the heat so it continues to boil gently. Allow the mixture to cook, stirring occasionally, until it sets, about 25 to 30 minutes. To test the set, place a saucer in the freezer for a couple of minutes, then drizzle a teaspoon of hot jam on it. Allow to cool, then run your finger through it. If it holds the trough, it's set. Also taste for sweetness at this point; if you think it could use more, add a bit more sugar and cook another minute or two; do the same with lemon juice if the acidity needs some perking up.
Pour into hot, sterilized jars, seal tightly and process according to your preferred canning method. Or simply keep in a closed container in the fridge for up to a month.
* recipe can be doubled
**please note: Molly used a combination of blood oranges and navel oranges for the recipe in the photo. If you're only using blood oranges, your results may look slightly different than the photo.
Original recipe adapted from: http://seattletimes.nwsource.com/html/pacificnw/2017567618_pacificptaste04.html