Blender Secrets: Inverted Hull Toon Outline (updated)
I decided to update this inverted hull video, since the interface of Blender 2.8 changed and a lot of people asked me where the Backface Culling option went.   So here we go. 
Create a base color material.   Go to Render View and increase the World brightness so you can see what you're doing!  Create a second material for the Outline.  You can use an Emission shader or Toon shader for the Outline material.  In the material settings, turn on "Backface Culling".  
Add a Solidify modifier, check "Flip Normals". Set the Material Index Offset to 1 and play with the Thickness to get the Outline. To render turn off Overlays and can go to View and choose "Viewport Render Image".

 
      