Rhubarb and Orange Marmalade

The following marmalade comes from Cooking with Tien: 

Ingredients:

3 cups of frozen or fresh rhubarb
2 cups of sugar
1 orange with seeds removed (diced to puree the whole orange with peel)

Method:

Combine rhubarb and sugar in a large heavy saucepan. Grind oranges, including the peels, in a food processor; add to rhubarb mixture. Bring to a boil. Reduce heat and simmer, uncovered, stirring often until marmalade sheets from a spoon, about 1 hour.

Pour into hot jars, leaving 1/4-in. headspace. Adjust caps. Process in a boiling-water bath for 10 minutes.