Make the shells first: pile small rounds of grated cheddar on a lined tray, well spaced, and bake at 200C/400F for six to eight minutes until the edges are golden and the middle is set but still floppy.
While each round is still warm and bendy, drape it over a wooden spoon handle or the rungs of an upturned rack so it sets into a taco shell shape as it cools.
Brown the mince hard in a dry pan in its own fat, breaking it small only once it has real colour. Do not drain the fat.
Salt at the end, and stir in the cumin and paprika now if you are using them.
Spoon the taco meat into the cheese shells, top with soured cream and more grated cheese, and eat straight away before the shells soften.