2 celery stalks (taken from the celery heart) with leaves, thinly sliced
1/4 cup (10 g) flat-leaf parsley leaves, coarsely chopped
1 tsp (5 ml) olive oil
In a small bowl, combine the egg yolk and water with a fork. Set the egg wash aside.
In a food processor, finely chop the bread into crumbs. Transfer to a large bowl. Add the milk. Mix and let soak for 5 minutes. Add the egg white and remaining ingredients, except for the lasagna noodles. Mix well with your hands. Season with pepper.
On a work surface, cut each noodle in half horizontally and then vertically to get four equal rectangles from each noodle. Place about 2 tbsp of the meat mixture along the short side of each rectangle. With a pastry brush, brush the empty side of each rectangle with the egg wash. Tightly roll each rectangle to seal in the filling. The cannelloni can be frozen at this step, if needed. Place the cannelloni, seam-side down, in a large, high-sided skillet.
With the rack in the middle position, preheat the oven to 350°F (180°C).
Meanwhile, in a pot, bring the broth and spices to a boil. Season with salt and pepper. Delicately pour over the cannelloni. Cover the skillet.
Transfer to the oven and bake for 15 minutes or until the filling is completely cooked through. Gently transfer the cannelloni to a large, lightly oiled plate. Cover with foil and set aside.
Return the skillet to the heat and bring the broth to a boil. Gradually sprinkle in the toasted flour while whisking. Cook until the sauce thickens. Adjust the seasoning.
In a bowl, combine all of the ingredients. Season with salt and pepper.
To serve, spoon the sauce over the cannelloni and garnish with the topping.