Prep: 30 minutes
Total: 1 ½ hours
8 cups white country bread, cubed into 1/2-inch squares
8 tablespoons unsalted butter
2 pounds yellow onions, peeled and thinly sliced
1 ½ teaspoons chopped fresh thyme
1 teaspoon kosher salt
½ teaspoon freshly ground black pepper
1 cup dry red wine
1 cup beef stock
¾ cup heavy cream
¾ cup whole milk
¼ cup chopped chives, plus more for garnish
4 large eggs
4 cups shredded gruyere cheese
1. Heat the oven to 350°F. Lay the cubed bread on a baking sheet and bake until lightly browned, about 15 minutes.
2. Melt the butter in a large skillet over medium-high. Add the onions, thyme, salt, and pepper and cook until brown, about 5 minutes. Reduce the heat to medium-low and cook, stirring often, until the onions are soft and caramelized, about 45 minutes. (If they look like they are going to burn you can add a few tablespoons of water to keep them caramelizing). Increase the heat to medium-high, add the wine, and cook until the wine has evaporated, about 5 minutes. Add the beef stock and bring to a boil, then reduce the heat to medium-low and simmer until thickened, about 5 minutes. Remove from heat and cool completely.
3. Meanwhile, whisk together the heavy cream, milk, chives, and eggs in a medium bowl. Fold in 3 cups of the gruyere. Add the cooled onion mixture to the custard base, stirring to combine, then add the bread cubes. Spray two 12-cup muffin tins with non-stick spray. Divide the mixture evenly among the tins. Set aside for 15 minutes to allow bread to soak up custard.
4. Place the muffin tins in the oven and bake for 20 to 25 minutes until bread puddings are golden brown and puffed. You can cool down and freeze the bread pudding cups at this stage. To reheat from frozen, heat the oven to 350°F and bake the bread pudding for 40 minutes before continuing on to step 5.
5. Disperse the remaining cup of gruyere on top of each pudding cup and broil for about a minute until the tops are golden brown. Remove from oven and let sit 5 minutes, then transfer to a serving platter and sprinkle with chives.