ShaderLab / writing custom shaders in URP

How do I go about writing custom shaders in Universal Render Pipeline in script / code / ShaderLab, without using Shader Graph? I do not want to get into the discussion why I do not want to use Shader Graph. Let's just say it is a personal preference and because Shader Graph does not play well with VCS, so please keep this discussion focused on how to work with URP and ShaderLab / hand-written shaders

Is there any official documentation or examples?

 

The built-in pipeline had Surface Shaders which were fairly well documented. We would like to do something similar but with URP.