Rehydrate dried mushrooms with 2 cups boiling water, about 30 minutes.

Drain, reserving liquid. Coarsely chop mushrooms, removing tough stems.

Preheat oven to 350°F. Line a baking sheet with parchment.

In a large skillet over medium heat, melt butter. When foamy, add shallots and garlic, and cook until tender, about 5 minutes.

Add mushrooms, and cook until golden, about 10 minutes.

Add wine, and cook until reduced by half, about 5 minutes. Add 1/2 the reserved mushroom broth and continue to simmer until almost dry, for about 10 minutes.

Whisk flour into remaining reserved broth, and add to mushroom mixture. Cook until well thickened, about 5 minutes.

Season with salt, pepper, and thyme. Remove from heat and set aside.

Roll out puff pastry to a form a rectangle about 12 x 18 inches. Spread mushroom filling down the middle of the rectangle, fold dough over to seal, and place on prepared baking sheet with the seam side down. Slash crosswise with a sharp knife or razor.

Bake 45 to 55 minutes, or until crust is golden brown.