Place flour in workbowl of food processor fitted with steel blade; add the 4 tablespoons butter; pulse until butter is absorbed, about 10 to 12 pulses of 1 second each.

Add remaining butter; pulse once or twice to distribute. Dissolve salt in water and add to flour mixture; pulse 3 or 4 times, until dough just starts to form a rough ball (see illustration 1, below) - do not overprocess. If mixture remains very dry, add a teaspoon of water at a time and pulse again.

Turn dough onto floured work surface and shape into rough rectangle, then place on top of sheet of well-floured plastic wrap measuring at least 12-by-18 inches. Lightly flour top of dough and cover with another sheet of wrap. Press dough with rolling pin to flatten, then roll back and forth several times with rolling pin to make 12-by-18-inch rectangle of dough.

Peel away plastic wrap and invert dough onto floured work surface, long side facing you. Peel away second piece of wrap. Fold top third of dough down and bottom third up (illustration 2), to make 4-by-18-inch rectangle, then roll up dough from one end (illustration 3). Divide dough in half and press dough into two squares, wrap in plastic and refrigerate 1 hour or until firm. You can reserve one square for other purposes or double the recipe.

Sprinkle ½ cup sugar on a work surface and roll one of the squares of puff pastry into a 12-by-9-inch rectangle. Slide onto a pan and refrigerate until firm, about 1 hour.

Remove dough from refrigerator and brush dough with egg beaten with a pinch of salt. Sprinkle remaining ½ cup sugar on dough. Fold each long side toward the center. Repeat folds so folded edges meet in the center, then fold in half at center. Wrap in plastic and chill until firm, about 1 hour.

Using a sharp, thin knife, cut dough into ½-inch slices; arrange cut side down on 2 parchment lined cookie sheets, about 2 inches apart on all sides.

Meanwhile, preheat oven to 350 degrees. Bake until golden and crisp, about 20 minutes. Cool on pans and serve at room temperature or reheated.