Potato, Tuna & Mushroom Gratin – adapted from a Julia Child potato gratin recipe. Potato, Tuna & Mushroom Gratin This Potato, Tuna & Mushroom Gratin is adapted from the recipe for Gratin of Potatoes, Onions and Anchovies from Julia Child’s infamous “Mastering the art of French Cooking“. The first time I cooked the Gratin, I […]