How to Make It
Spray a 5-quart slow cooker with baking spray.
Whisk together sugar, flour, cocoa, baking powder, baking soda, and salt in a large mixing bowl until combined. Add oil, vanilla, eggs, and 1 cup of the milk; stir to combine. Stir in boiling water just until combined. Pour cake batter into prepared slow cooker.
Whisk together pudding mix and remaining 2 cups milk in a medium bowl until smooth. Let stand until slightly thickened, about 5 minutes. Pour pudding in center of cake batter in the slow cooker. Sprinkle evenly with chocolate chips.
Place lid on slow cooker, and cook on HIGH until cake is dry to the touch, about 2 hours and 30 minutes. Serve with ice cream.