Peel and chop the potatoes and boil in seasoned water for 20 minutes until soft.
While they are cooking, wash and drain the sorrel, removing the stalks, and melt in the fat over a low heat with the garlic and herbs. By the time the potatoes are ready, the sorrel mixture will have reduced to a smooth purée. Stir in the flour.
Liquidize or sieve the potatoes with their water and s