The photographs in the cookbook Cézanne and the Provençal Table (Clarkson Potter, 1995) lured us in, but the recipe omitted several key ingredients. Here's how we got it to work.
1⁄2 lb. sliced mixed fresh mushrooms, such as criminis
and wild chanterelles
1 large yellow onion, peeled and sliced
1 tsp. sugar
1⁄4 cup extra-virgin olive oil
3 scallions, trimmed and chopped into 1" pieces
2 cloves garlic, peeled and minced
1 tbsp. red-wine vinegar
Salt and freshly ground black pepper
Leaves from 4–5 sprigs flat-leaf parsley, chopped
1. Clean mushrooms with a damp cloth, trim stems, and slice. Cook onions with sugar in oil in a 9" skillet over low heat until caramelized, about 30 minutes. Add mushrooms, scallions, garlic, and vinegar, and cook another 10 minutes. Remove half the mixture and set aside.
2. Preheat oven to 350°. Whisk eggs with 1 tbsp. water in a medium bowl and season with salt and pepper. Raise heat to medium-low; add eggs to mushroom mixture in skillet. Tilt pan and use a wooden spoon to gently draw the uncooked egg towards center of skillet. When eggs are still a bit runny, top with parsley and reserved mushroom mixture; finish omelette in oven, 3 minutes. Serve at once.