Step 1

Wash oranges well. Use a peeler to remove all the zest in long strips. It's okay if some of the white pith comes with it.

Step 2

Transfer the peels to a saucepan and add 6 cups of cold water. Bring to a simmer over high heat. Reduce heat to medium-low to low and simmer until the peels are soft and tender, 45 minutes to 1 hour.

Step 3

While that cooks, cut oranges in half and juice them into a large measuring cup; this should equal 1 cup. Pour in 1/2 cup cold water and set aside.

Step 4

Remove peels from heat and drain off the water. Transfer peels to a cutting board, and when cool enough to handle, slice the zest into very thin strips. Transfer into the blood orange juice.

Step 5

Pour zest-juice mixture into the saucepan along with lemon juice and sugar. Bring to a simmer over medium-high heat. Reduce heat to medium-low; cook, stirring occasionally, until the mixture reduces and thickens slightly, 30 to 40 minutes. A probe or candy thermometer should read about 225 degrees F (107 degrees C).

Step 6

Meanwhile, inspect jam jars for cracks and rings for rust, discarding any defective ones. Immerse in simmering water until juice mixture is ready. Wash new, unused lids and rings in warm soapy water.

Step 7

Pour into sterilized jam jars and let cool to room temperature. Seal jars and transfer to the refrigerator for 8 hours, or overnight, before enjoying.