Coulibiac with dill sauce

Rice, long-grain white	½ cup
Butter, unsalted	2 tablespoons
Leeks, white & pale green parts only, minced	½ cup
Mushrooms, shiitake, stemmed, chopped	6 ounces
Salt
Pepper, freshly ground
Puff pastry, thawed	17 ¼ ounces
Salmon fillet, skinless, cut into 4 ounces pieces	24 ounces
Egg, beaten	1 large
Water	1 tablespoon
Clam juice	2/3 cup
Wine, dry white	½ cup
Crème fraîche	1 ¼ cups
Dill, fresh, minced	3 tablespoons

1. Bring a medium saucepan of salted water to a boil. 
2. Add the rice; boil uncovered until just tender, about 18 minutes; drain. 
3. Melt the butter in a medium skillet over medium-low heat. 
4. Add the leek and sauté until beginning to soften, about 4 minutes, and then add the mushrooms. 
5. Cover the skillet, and cook until the mushrooms release their juices, stirring occasionally, about 5 minutes; uncover the skillet. 
6. Increase heat to medium-high, and sauté until the liquid evaporates, about 3 minutes. 
7. Transfer to a bowl with the rice; season with salt and pepper, and cool completely. 
8. Butter a large baking sheet. 
9. Roll out one pastry sheet on a floured surface to 12-inch square; cut into four equal squares. 
10. Divide the rice mixture among the centers of each square, mounding in an oval shape with ends pointing toward two corners of the pastry. 
11. Set the salmon atop the rice, and sprinkle with salt and pepper. 
12. Bring the pastry corners up around the salmon (the pastry will not enclose the salmon completely). 
13. Roll out the remaining pastry on a floured surface to a 13-inch square. 
14. Cut into four equal squares. 
15. Lay one square atop each salmon fillet, tucking corners under the bottom pastry to enclose the salmon completely. 
16. Combine the egg and 1-tablespoon water in a small bowl. 
17. Pinch the edges together to seal, brushing with the egg wash, if necessary, to adhere. 
18. Arrange the salmon packages, seam side down, on the prepared baking sheet. 
19. Cover and chill for 30 minutes. (Can be made 8 hours in advance; keep chilled.) 
20. Preheat the oven to 400°F. 
21. For the sauce, combine the clam juice and wine in a small saucepan. 
22. Boil until reduced to 1/3 cup, about 9 minutes. 
23. Reduce heat to medium, and whisk in the crème fraîche. 
24. Boil until reduce to 1 cup, about 5 minutes; remove from heat. 
25. Stir in the dill; season with salt and pepper. 
26. Brush the top of each pastry with the egg wash. 
27. Bake until golden and a thermometer inserted into the fish registers 145°F, about 30 minutes. 
28. Serve with the dill sauce and a glass of chilled champagne.