How to Make It
Bring 1 1/2 cups water to a boil in a small saucepan. Add porcini mushrooms; remove from heat, and let stand 30 minutes. Drain through a sieve over a bowl, reserving soaking liquid. Finely chop mushrooms and set aside.
Meanwhile, preheat oven to 400°F.
Line 2 baking sheets with parchment paper. Combine potatoes and 2 teaspoons oil in a bowl, tossing to coat. Arrange potato slices, slightly overlapping if necessary, on prepared baking sheet. Repeat procedure with 2 teaspoons oil and butternut, and 2 teaspoons oil and purple sweet potatoes, arranging on prepared baking sheets. Roast at 400°F for 25 minutes or until tender. Remove pans from oven; let cool to room temperature. Turn oven off.
Meanwhile, wrap beets in microwave-safe parchment paper. Microwave on HIGH for 6 to 8 minutes or until tender. Let cool to room temperature. Rub off skins, and cut beets into 1/4-inch-thick slices.
Bring a large pot of water to a boil. Add chard; boil 2 minutes or until bright green and tender. Drain and rinse with cold water. Squeeze out most of water, leaving some moisture. Fluff chard to loosen the texture.
Place crimini mushrooms in a food processor; pulse until finely chopped. Heat 1 tablespoon oil in a large nonstick skillet over medium-high. Add 1/3 cup shallots; sauté 2 minutes. Add garlic; sauté 30 seconds. Add crimini and porcini mushrooms; cook until liquid mostly evaporates, about 8 minutes, stirring occasionally. Stir in 1 tablespoon thyme, 1/8 teaspoon salt, and 1/8 teaspoon pepper. Add goat cheese, stirring until cheese melts; cool slightly.
Line a 9 x 5–inch loaf pan with plastic wrap, extending over edges of pan. Place puff pastry on a lightly floured work surface. Roll to a 15 x 12–inch rectangle; cut off 1 inch from a long side to form a 14 x 12–inch rectangle. Set trimmed dough aside. Fit dough into loaf pan, allowing edges to extend over edges of pan. Layer Yukon gold slices into pan; sprinkle with 1/8 teaspoon salt and 1/8 teaspoon pepper. Top with butternut slices; sprinkle with 1/8 teaspoon salt and 1/8 teaspoon pepper. Top with beet slices; sprinkle with 1/8 teaspoon salt and 1/8 teaspoon pepper. Arrange chard over beet slices. Top with purple sweet potato slices; sprinkle with 1/8 teaspoon salt and 1/8 teaspoon pepper. Carefully spread mushroom mixture over sweet potato slices. Carefully bring dough edges up and over mixture; pinch to seal edges along length of the loaf. Carefully lift top of loaf using plastic wrap; pinch to seal end seam. Carefully lift bottom of loaf using plastic wrap; pinch to seal end seam. Place loaf, in the pan, in freezer for 30 minutes.
Roll out dough trimmings, and cut with a leaf-shapped cutter, if desired. Place dough strips in freezer.
Preheat oven to 425°F.
Carefully invert loaf onto a parchment paper–lined baking sheet. Remove and discard plastic wrap. Brush top and sides of loaf with egg. Arrange leaf cuttings, if using, on top of loaf. Brush leaf cuttings with egg. Bake at 425°F for 30 minutes or until well browned. Carefully lift loaf, with parchment, off pan and place on a wire rack to cool. Cool at least 10 minutes before slicing.
Heat remaining 2 tablespoons oil in a medium skillet over medium-high. Add remaining 2 tablespoons shallots; sauté 1 minute. Stir in flour; cook until lightly browned, about 1 to 2 minutes. Slowly pour in mushroom soaking liquid, stopping before any grit in the bottom of the bowl escapes (discard grit). Stir in wine. Cook until slightly thickened, about 2 minutes, stirring constantly. Stir in soy sauce and remaining 1 1/2 teaspoons thyme, 3/8 teaspoon salt, and 1/8 teaspoon pepper.