How to Make It
Preheat the oven to 350°. Generously butter a 12-cup muffin tin. Spread the pine nuts in a pie plate. Toast the nuts for about 4 minutes, until golden.
Spread the brioche cubes on 2 large baking sheets. Bake for about 15 minutes, until toasted. Transfer to a large bowl and let cool. Increase the oven temperature to 375°.
In a large skillet, heat the oil. Add the onion and celery and cook over moderate heat until softened, 5 minutes. Add the mushrooms and season with salt and pepper. Cover and cook, stirring, until the mushrooms are tender and browned, 7 minutes. Let cool, then add to the brioche.
In a medium bowl, whisk the cream with the eggs. Stir in the stock, lemon zest and juice and 2 teaspoons of salt. Add to the brioche along with the parsley and toasted pine nuts and stir well. Spoon the stuffing into the prepared muffin cups. Bake in the upper third of the oven for about 45 minutes, until crisp on top and heated through. Unmold and serve hot.