In a small bowl, combine pudding mix and cold milk. Beat with a whisk until completely smooth and no lumps remain. Let mixture stand at room temperature for about 5 minutes. It should thicken into a pudding.
Preheat oven to 350°F. Prepare four (4-oz) ramekins by spraying with PAM with flour. If you don't have an oil spray with flour, you can also grease inside of ramekins, sprinkle generously with flour, then tap ramekins to get rid of excess flour
In a large mixing bowl, add chopped chocolate and milk. Microwave for about 1 minute (be sure to cover the bowl with a microwave-safe paper towel). Stir with a whisk until chocolate is mostly melted.
Microwave again for an additional 1 minute and stir until melted chocolate is completely uniform. You can also melt chocolate with milk on the stove, over a pot of simmering water.
Add in remaining cake ingredients. Whisk until batter is completely smooth.
Add batter into prepared ramekins, until they are about half full. Add 2 tbsp of Oreo pudding to the center of each ramekin. Evenly divide remaining batter between the four ramekins, making sure to completely cover the oreo filling.
Cakes will not rise too high during baking, so if they are about 2/3- 3/4 full, it is fine.
Place ramekins on a baking sheet. Bake for 17-18 minutes, or until the surface of cakes are just set.
Remove cakes from oven. Use a small spatula to dislodge the sides of the cakes from the ramekins. Place a small plate on top of each ramekin.
Very quickly, invert the plate with ramekin, so that the plate is now on the bottom and the ramekin is upside down on top. When you lift up the ramekin, the cake should be on the plate. Repeat with remaining ramekins. Serve immediately.