Cake:
1 box chocolate cake mix
1 cup milk
1/2 cup vegetable oil
3 eggs

Topping:
1 (3.9-ounce) box chocolate instant pudding and pie filling mix
2 cups cold milk
1 (11.5-ounce) bag milk chocolate chips

Spray 6-quart slow cooker with cooking spray. In a large bowl, beat cake mix ingredients with a mixer on medium speed for 2 minutes. Pour into a slow cooker. In a medium bowl, beat pudding mix and milk with a whisk for about 2 minutes or until thick. Pour into the slow cooker over the cake batter mixture. Do not mix. Sprinkle all chocolate chips on top. Do not mix. Place lid on slow cooker and cook on low for 3 to 3.5 hours or until cake is set around the edges but still soft in the center.