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["Heat oven to 200u00b0F with racks in upper and lower thirds. Line 2 large baking sheets with parchment paper.", "Beat egg whites with cream of tartar and salt in bowl of stand mixer on high speed until they just hold soft peaks. Beat in sugar, 2 tablespoons at a time, beating well after each addition, and continue to beat at high speed until meringue is very stiff, about 2 minutes. Beat in vanilla and beat again until very stiff.", "Sift cocoa over meringue, and fold it in gently but thoroughly.", "Spoon meringue into a pastry bag fitted with tip. Holding bag vertically, about 1/2 inch above baking sheet, pipe meringue into 25 mounds, ranging in size from about 1 1/2 to 2 inches in diameter, to resemble mushroom caps.", "Still holding pastry bag vertically, pipe remaining meringue vertically into 25 ""stems,"" 1 1/4- to 1 1/2 -inch-long lengths (make different lengths), making each base about 1 inch in diameter and tapering top end by pulling up on bag. (Pipe extra caps and stems with any remaining meringue in case of breakage.)", "With a finger dipped in water, gently tamp down any peaks of meringue on caps to make a smooth mushroom cap.", "Bake, switching position of sheets halfway through, until mushrooms caps are crisp and firm to touch, about 1 hour 45 minutes.", "Turn off oven, then leave meringues in oven, with door closed, 30 minutes to dry. Slide parchment with meringues from baking sheets onto racks to cool. Cool completely.", "With tip of a sharp paring knife, cut a small hollow the diameter of the tapered top of mushroom ""stem"" in center of the underside (flat side) of each mushroom cap.", "Spread chocolate generously over flat bottom of a cap with offset spatula or back of spoon, then insert narrow end of stem. Let cap rest, stem end up, on a tray or baking sheet. Attach remaining stems to remaining caps, and let stand, stem ends up, at cool room temperature until chocolate is set, about 1 hour."]
