The Vegemite Sandwich is australian yeast extract; similar to Marmite but different recipe, served as a regional specialty in UK (Australian influence).
It sits within the Tartines family of French sandwiches — specifically the On Toast & the Open-Face Savoury cluster, which gathers the regional and stylistic variants that share its frame.
For the broader On Toast & the Open-Face Savoury tradition that frames this sandwich, see On Toast & the Open-Face Savoury.