Combine pineapple juice, brown sugar, ketchup, soy sauce, garlic, worcestershire sauce, and spices in a large measuring cup or mixing bowl. Mix until all ingredients are incorporated, then set aside.
Heat 2 Tbsp. butter in a large skillet over medium-high heat.
Add chopped onion and saute until onion begins to brown.
Stir in ΒΌ c. flour.
Pour pineapple juice mixture into skillet and boil, stirring, 10-15 minutes or until sauce is thick.
Place chicken in slow cooker and cover with sauce.
Cook on low heat 8 hours.