Bring 1 3/4 cups apricot nectar and spices to a boil in a small saucepan over high heat, covered. Reduce heat and simmer 10 minutes. Strain, then measure 1 1/4 cups, adding more juice if needed.
Combine pectin and 1/4 cup sugar in a 5- to 6-qt. pot. Stir in plums, then spiced juice, lemon juice, and butter. Bring to a brisk boil over high heat, stirring often.
Add remaining 1 1/4 cups sugar. Return jam to a brisk boil, stirring. Cook, stirring constantly, 1 minute. Remove from heat.
Ladle jam into heatproof jars, distributing fruit evenly, and close with lids. Let cool to room temperature, inverting jars occasionally to distribute fruit. Keeps, chilled, up to 1 month.
*We used Santa Cruz Organic Apricot Nectar.
Note: Nutritional analysis is per tbsp.