It’s a plot point, and the recipe is not in the book, although others for sole are, helpfully indexed under “poisson.”)
If after 26 years of cooking for a living, I am worn out just reading those recipes, I can only imagine how a newbie who can barely identify a whiskwill do, let alone how someone who has never seen Dover sole in his supermarket could cook sole meunière, the other iconic Julia dish that restaurants and home cooks have been reflexively celebrating since ogling it in the film. It’s a plot point, and the recipe is not in the book, although others for sole are, helpfully indexed under “poisson.”)