1. Prepare the kidneys by rinsing them thoroughly in cold water then patting them dry with kitchen paper. Split each kidney in half longways and cut out and discard the white core – we find using scissors to be the easiest way. Cut each half kidney in half again.
2. Put a tablespoon of flour and a pinch each of salt and pepper into a plastic food bag or bowl. Add the kidneys and give them a toss until they’re well coated with flour.
3. Add a generous knob of butter to a hot frying pan and let it melt and turn foamy. If you want to add onion, throw some in at this stage, frying it gently for 3 to 4 minutes until it’s softening and turning golden.
4. Making sure the butter’s foamy, shake any excess flour off the kidneys and add them to the pan. Let them sizzle for a minute or so per side so they start turning deliciously brown.
5. Working quickly, add a dollop of mustard to the pan – how much you use will depend on quite how devilish you want your kidneys to be. If you’re using tomato puree, add a squirt at this stage. Follow with about 300ml of boiling water, stirring constantly and letting it bubble with the mustard. Add cayenne pepper, Worcestershire sauce and seasoning to taste.
6. Reduce the heat and simmer the sauce for 12 to 15 minutes, stirring occasionally, until it thickens. Make sure you have a taste, adding more Worcestershire sauce, cayenne or seasoning.
7. Serve immediately on a slice of buttery sourdough toast while the kidney’s piping hot.
Fan of offal? Why not give our recipe for ox liver paté with balsamic onions a try?