Kidneys can have a reputation for tasting bad. Bathroom bad. However, the flavor of kidney can be improved greatly with proper cleaning and preparation.
Remove any exterior fat and membrane, if present.
Place the kidney on a cutting board with the white vein facing up. Slice the kidney in half lengthwise straight through the white vein. Once cut in half, you will see where the vein enters the kidney and fans out inside.
Use a small, sharp knife or scissors to cut away all of the white vein from the interior of the kidney. Once trimmed you should be left only with dark kidney meat.
The kidney is now ready for your next steps in preparation. If desired, the kidneys can be soaked in milk for a few hours or overnight to soften some of their flavor even more.