Slow Cooker Molten Chocolate Peanut Butter Cake

12 TBSP butter, melted ( two to coat slow cooker, 10 in with cake mix)
1 box devil's food chocolate cake mix
1 box instant chocolate pudding mix
1 C. peanut butter
1 (8 oz) container sour cream
1 C. milk
4 eggs
1 C. chocolate chips (or a combination of chocolate and peanut butter chips)

Evenly coat bottom and sides of 5 qt.* slow cooker with 2 TBSP melted butter; set aside.

Combine remaining ingredients except chocolate chips in large bowl with electric mixer, stir in chocolate chips and pour into prepared cooker.

Arrange two sheets paper towels over top of cooker, then place lid on top (paper towels will absorb moisture).

Cook on Low 3 1/2 hours. Turn off heat, then let stand covered 30 minutes. Remove insert from cooker. Carefully remove lid and paper towels. Serve cake warm and, if desired, with vanilla ice cream,

*If using 6 qt. slow cooker, cook on Low 4 1/2 hours, still letting stand for 30 minutes after that.