1. Cut the duck breast into small pieces. Soak the bread in the cream.
2. Heat the oil in a pan over medium heat. Add the shallots and chopped garlic and sauté until they soften. Add the duck, cook for 2-3 minutes, add the Muscat and deglaze for a few minutes. Add the walnuts, bread, and cream, and mix. Let cool. Mix in a food processor until a coarse mixture is obtained.
3. Meanwhile, melt the butter in a pan over medium heat, add the mushrooms and sliced garlic and sauté until they soften, about 4-5 minutes.
4. Preheat the oven to 200C/gas 6. Roll out the puff pastry into a 30 cm circle, cover with the prepared mixture, and top with the mushrooms. Bake in the oven for 25 minutes. Remove the tart from the oven, sprinkle with sea salt, cut into slices, and serve immediately.