2 large Vidalia onions, thinly sliced
3 tablespoons unsalted butter
2 tablespoons olive oil
⅓ cup apple brandy or Calvados
16 ounces vegetable stock
8 ounces cremini mushrooms, cleaned and sliced
2 carrots, cleaned and cut into coins
1½ tablespoons thyme
3 tablespoons all-purpose flour
1 sheet frozen puff pastry, thawed
Fresh, chopped chives, to garnish (optional)
Kosher salt and freshly ground black pepper
In a large skillet, heat two tablespoons of butter and one tablespoon of olive oil over medium-high heat. Add the sliced onion to the skillet. Sauté the onions until they start to cook down, stirring frequently. Onions will become translucent and lightly browned, about 6-8 minutes.
Reduce the heat to medium, and continue to let the onions cook down and caramelize, stirring occasionally, until the onions have developed a deep nutty color, about 20 minutes.
Add the apple brandy to the skillet, and stir to mix into the onions and deglaze the pan, about 1 minute. Cooking will also burn out the alcohol in the brandy. Remove from heat and transfer the onions to a large bowl. Set aside.
Return the same skillet to the stovetop, and melt the remaining tablespoon of butter and oil together over medium-high heat.
Add mushrooms and carrots to the skillet, and sauté together until the vegetables have softened, about 5-7 minutes.
Add thyme to the skillet, and cook until fragrant, about 1 minute.
Add flour to the skillet one tablespoon at a time, stirring constantly with the vegetables, until all the raw flour is cooked out, about 1 minute.
Add vegetable stock to the skillet, and stir to combine until thickened, about 3-5 minutes. Add the reserved onions to the skillet, and bring back up to temperature by simmering in the sauce. Taste and adjust seasoning with salt and pepper. Allow the flavors to blend by simmering for 3-5 minutes. Remove from the heat.
Transfer the onion mixture to the bottom of a baking dish (round or square).
Cover the baking dish with the puff pastry, making sure the sheet extends beyond the entire rim. Press down on the pastry around the rim to form a seal, and cut away the excess pastry with a knife. Cut three slits in the top of the pastry to vent while cooking.
Place the baking dish in the oven, and allow to bake until the crust is golden brown and the sides of the pie are bubbling, about 15-20 minutes.
Remove the pie from the oven, and allow to cool 5-10 minutes. Garnish with fresh, chopped chives (optional). To serve, scoop into individual bowls using a ladle, or serve out whole pies for people to scoop themselves.
Pro-tip: Make this dish even more like traditional French onion soup by replacing the puff pastry with sliced sourdough bread.
Pro-tip: For nonvegetarians, add another layer of flavor by using beef stock or beef consommé instead of vegetable stock.
