1. Preheat your oven to 425°F or 220°C.

2. Clean the mushrooms thoroughly and slice them into fine pieces. Sauté them in a generous amount of butter over medium heat until the liquid has completely evaporated. Set a few mushroom slices aside to be used for garnish later.

3. Sprinkle a pinch of flour over the mushrooms in the pan and stir well to combine. Gradually add in milk, stirring continuously to avoid lumps. Bring the mixture to a boil, then reduce the heat and let it simmer gently for 5 minutes.

4. Add heavy cream and a dash of soy sauce to the mushroom mixture, stirring well to combine. Season the mixture with salt and pepper to your taste, then let it simmer for an additional 5 minutes.

5. Arrange slices of bread on a baking sheet lined with parchment paper. Cut the brie cheese into small, bite-sized pieces. Place a piece of brie on each bread slice, followed by a spoonful of the mushroom mixture, and finally top with another piece of brie.

6. Place the baking sheet under the broiler and let it cook for 5 minutes, or until the cheese has melted and bubbled. Remove from the oven and sprinkle with parsley and the reserved mushroom slices.

7. Serve hot, accompanied by a fresh side salad and cherry tomatoes.