• Have a glass of ice water standing by and cut the butter into 16 pieces.

To mix the dough in a food processor:

• Place the steel blade into the work bowl of your food processor and add the flour, sugar, and salt.
• Scatter the butter over the flour. Using the pulse function, process until the mixture is coarse and crumbly, with visible pieces the size of very small peas.
• Sprinkle the mixture with 3 tablespoons of ice water and pulse until the dough comes together, adding water in teaspoon increments as needed. Be careful not to over-process.

To mix the dough by hand:

• Whisk the flour, sugar, and salt together in a large mixing bowl and add the butter pieces.
• Using your fingertips (or a pastry cutter), work the butter into the flour mixture until it's coarse and crumbly with visible pieces the size of very small peas.
• Make a well in the center and add 3 tablespoons of ice water. Mix with your fingertips, adding ice water by the teaspoonful, until the dough holds together well enough to form a ball.

Chill the dough:

• Transfer the dough to a sheet of plastic wrap. Using your hands, flatten it into a circle about 8-inches in diameter, wrap tightly, and refrigerate for 1 hour. (At this point the dough can be frozen for up to 6 weeks and thawed in the refrigerator before use.)

Prepare the pear filling:

• While the crust is chilling, combine the sliced pears, cinnamon, lemon juice and salt in a large bowl. Toss gently until the pear slices are coated with the cinnamon. Cover and set aside.

Roll the dough:

• Position a rack in the center of the oven and preheat to 400°F.
• Cut two pieces of parchment paper large enough to line a rimmed baking sheet and dust one of them lightly with flour. Place the chilled dough on top, dust that with flour as well, and place the other piece of parchment on top.
• Gently roll the dough from the center out, to a diameter of 12 to 13 inches, dusting with a little additional flour to prevent sticking as you go. Carefully remove the top sheet of parchment and slide the bottom one onto the baking sheet.

Assemble the galette:

• Starting in the center, arrange the pear slices in a casual spiral pattern several layers thick, making sure to leave a 2-inch border all around. Gently fold the crust over the filling, pleating it loosely.
• Whisk the egg and water together in a small bowl to make a wash, then brush over the edges of the galette and sprinkle with sugar.

Bake and serve:

• Loosely tent the top of the galette with foil. This will prevent the edges from getting too brown and help to tenderize the pears. Bake for 25 minutes, then remove the foil, rotate the baking sheet, and continue baking for an additional 20 to 25 minutes, or until the crust is crisp and golden and the pears are tender.
• Transfer to a rack and cool for about 20 minutes before cutting into wedges. Top with fresh whipped cream or ice cream if desired.