Combine the chocolate cake mix, sour cream, vanilla, butter,eggs and 1 ¼ cups of milk in a large bowl (or directly in the crock pot);Transfer to slow cooker.
In a separate bowl, combine the pudding and remaining 2 cups of milk and whisk as directed on the package.
Pour directly on top of the prepared cake mix. Do not stir.
Secure the crock pot lid and cook on high for 2 hours or low for 4 hours.
Remove the lid and sprinkle on the mini marshmallows and chocolate chips.
Put the lid back on and allow to cook for 15 minutes.
Notes
Double: Great recipe for a crowd. Simply increase the ingredients proportionately and split it into two crock pots.
Add Nuts: Add walnuts or pecans for a nice crunch.
Finish: A scoop of Vanilla ice cream adds a cool finish.
Variation tip: Top with fresh fruit such as berries and a little powdered sugar and cocoa powder.
Alternate ingredient: Finish with a caramel sauce on top of the cake.
Alternate cooking method tip: Can cook in the instant pot. Cook for nine minutes and do a quick pressure release.