Miche wrote:

I don't think I have ever put stock cubes into gravy. Salt, yeah, but
not stock cubes (which are just meat-flavouring flavoured salt, anyway).

Maybe not stock cubes, but commercial demi-glace of various kinds (e.g.
Aromont products), Liebig meat extract (3 kg meat per 100 g extract), or
Englert meat or chicken extract (respectively 3 kg meat or 2 kg chicken
per 100 g extract) are used often enough. They all happen to be in the
form of paste but could very well be marketed as stock cubes.

Victor