So I toasted two slices and made a tea. In one of the slices I spread butter and in the other marmite (yeast extract). I never tried it before but last week I saw a documentary in BBC where they tried to make home made yeast extract: basically they kill the yeast with salt (one thing that bread makers try to avoid religiously every time they make the dough) and to help the process they heat up the mix, so the result is a dark brown and very (very) salty sticky paste, with umami qualities. It is usually eaten as a savoury spread in bread and toasts or to give flavour to stews as a vegetarian alternative to beef extract.
It was delicious with the butter, and interesting with the marmite, as even very thin layer was enough to give a very strong and salty flavour to the bread.