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["Cut dough in half and chill 1 half, wrapped in plastic wrap.", "Roll out remaining half on a lightly floured surface, dusting with flour as necessary, into a 16 1/2- by 7-inch rectangle.", "Brush off excess flour with pastry brush and trim edges with a pizza wheel or sharp knife.", "Cut dough into quarters, forming 4 rectangles.", "Arrange 1 rectangle with a short side nearest you.", "Gently score rectangle twice vertically to divide lengthwise into thirds, but do not cut through.", "Now cut ""fringe"": Along each long side, make an equal number of horizontal cuts, 1/2 inch apart, with scissors, cutting from edge to closest score mark and leaving middle of rectangle uncut.", "Slightly overlap 2 slices prosciutto on a work surface to form a 6-inch-long piece and sprinkle with 2 teaspoons cheese and pepper to taste.", "Roll up prosciutto, enclosing cheese, to form a 6-inch-long log, then place log down center of fringed rectangle, between scored lines.", "Working quickly with fringe, braid by making a crisscross pattern over prosciutto similar to that made by lacing a shoe: Take top right strip and, stretching dough slightly, cross it over prosciutto to left side, pressing it onto base of second strip (from top) so that strip adheres.", "Cross top left strip over to right side in same manner.", "Continue crossing strips until you reach bottom, then tuck last 2 strips under bottom edge of dough, pressing to adhere.", "Put braid on a parchment-lined large baking sheet.", "Make more braids with remaining 3 rectangles, then with chilled dough, arranging 2 inches apart on baking sheet.", "Slide baking sheet into garbage bag, propping up top of bag with inverted glasses to keep it from touching pastries, and tuck open end under baking sheet.", "Let pastries rise until slightly puffy and spongy to the touch, 2 to 2 1/2 hours.", "Set oven rack in middle of oven and preheat to 425F.", "Remove baking sheet from garbage bag.", "Lightly beat yolk with a few drops of water to make a glaze.", "Brush braids with some glaze and sprinkle with sesame seeds.", "Spritz inside oven generously with spray bottle and close door.", "Put braids in oven, then spritz again before closing door.", "Reduce temperature to 400F and bake 10 minutes without opening door.", "Rotate baking sheet 180 in oven, then reduce temperature to 375F and bake until braids are deep golden, 12 to 15 minutes more."]
