Put a tablespoon of the cream in a bowl and add the espresso and cocoa powder. Mix these together until both powders are completely dissolved and there are no lumps. Have patience here, it takes a couple of minutes for the little grains of instant coffee and cocoa powder to fully dissolve.
Add the rest of the cream, while stirring, or gently whisking.
Add the whiskey, vanilla, and condensed milk and blend everything well. Note: alternatively you can put everything in a blender and blend briefly. Blend just long enough to combine.
Take a taste ~ this is now your own custom liqueur, adjust any of the ingredients to your liking.
Pour the mixture into a clean bottle with a top, and refrigerate until needed.
This will keep in the fridge for at least a couple of months, and probably longer, but I'm pretty sure you will polish it off before then ;)
Video
Notes
Lighten up your homemade Irish Cream by using half and half instead of heavy cream.
If you want a less potent liqueur just reduce the whiskey.
Add more espresso or more cocoa powder to change the flavor profile to your particular liking.