Halve grapes lengthways, core. Drain the butter in a pan, toss the grapes in it until they are hot. Remove and keep warm.
Now fry the floured liver cut into bite-sized pieces in the pan, adding salt and seasoning with freshly ground pepper. Add pieces of liver to the grapes, keep warm. Allow the finely diced shallots to become translucent in the pan. Now deglaze with the Madeira and reduce a little. Add the grapes with the liver, briefly heat again and toss, serve immediately.
With baguette and a well-chilled Riesling or Pinot Gris.