Recipe Courtesy Anna and Michael Olson.The origin of this dish takes us into the baker’s kitchen. After a hard night’s work in front of his wood-fired oven, the French baker (boulanger) would put his terra cotta dish of potatoes and onions into the oven while he finished his work, and dinner would be ready at the end of his day (and the start of everyone else’s.)
Preheat oven to 350 °F (180 °C). Butter an 8-cup (2 L) baking dish with 1 Tbsp butter and rub with garlic. Set aside.
In a sauté pan over medium heat, add remaining 2 Tbsp butter and olive oil and add onions. Cook until, stirring often, until they are a rich golden brown colour, about 20 minutes. Add sherry and tarragon and cook until liquid is absorbed. Remove from heat and season to taste.
Arrange a layer of sliced potatoes in the bottom of baking dish, season lightly and top with about 1/3 cup of caramelized onions. Arrange another layer of potatoes over onions, and repeat process until all potatoes and onions are used, finishing top with potatoes. Bring chicken stock up to a simmer and pour slowly over potatoes. Cover dish with parchment and then foil and bake for 40 minutes. Uncover dish and bake 20 minutes more, until potatoes are tender (test by inserting a knife into dish – potatoes should feel tender). Let cool 10 minutes before serving.