2 Blending brushes
These are the blending brushes I made called "Double Cheeseburgur". Here are some examples for correct usage of the 2 brushes.
First thing I did was to put down the shading with my "Soda" brush (you can get that one for free) and then I just blended the mess together with "Double cheeseburgur" to give the shadows a rough shape. Afterwards I used "Double Cheeseburgur Soft" to give the shadows a little bit of smoothness.
You don't have to use the "Soda" brush for the shadows and can use any other brush you like, it'll still work.
Double Cheeseburgur