Preheat oven to hot 220ºC / 200ºC (fan-assisted)
Heat oil in small frying pan; cook onion, stirring, until softened. Blend or process onion with
beans until almost smooth; return to same pan. Add salsa and soured cream; stir until heated
through. Place tortilla triangles onto lightly oiled baking trays; top with bean mixture and
Bake tostadas until cheese melts; serve topped with fresh coriander leaves, if desired.