In a medium-size microwave-safe bowl, stir marmalade with soy sauce. Microwave, uncovered, on high until softened, 1 minute.
OR melt in a saucepan, stirring often.
Stir in barbecue sauce.
Place chicken in crock pot. Pour in sauce. Stir to coat.
Cover and cook on high setting 4 hours or low 6 hours.
To bake, preheat oven to 350F (180C). Place chicken in a large, ovenproof casserole dish that will hold at least 16 cups (4 L). Pour sauce over chicken. Stir to evenly coat. Set on a baking sheet to catch any drips if it bubbles over.
Bake, covered, in centre of preheated oven until chicken feels springy when pressed and sauce is bubbly, about 1 3/4 hours.
To thicken sauce, remove cooked chicken to a large serving bowl.
In a small bowl, stir cornstarch with water until dissolved.
Carefully ladle liquid from slow cooker or casserole into a medium-size saucepan.
Set over high heat. Bring to a boil. Stir in cornstarch mixture.
Reduce heat to medium. Stir until sauce thickens, 2 minutes. Pour over chicken.
Note: I prefer orange marmalade, ginger marmalade can be substituted. Recipe yields approximately 3 cups of sauce.