I’m wondering how to make a parameter in config.toml that is something like logo = "{{ .baseUrl }}/images/logo.png"
The reason is because maybe I want to use an external source graphic instead and I don’t want all the logo references in my layouts to have to have {{.baseUrl }}{{.Site.Params.logo}} hardwired into them.
or is there another way to reference a parameter in config.toml from within the same file?
No…
Use the absURL and relURL functions. I wouldn’t recommend manually adding baseURL to construct URLs in your templating.
Generally, configuration files are completely logic free, so it might be best to aim for simplicity to in your key-value pairs and then add complexity/relationships/logic in the templating layer. Just a thought 
I totally agree. the problem is the theme is not my theme. So it came that way.
Ah, gotcha. Perhaps an issue in the theme’s GH repo then? 