Preheat the oven to 400°F. Line a sheet pan with parchment paper.

Roll the pie dough into a 12'' circle (it doesn't have to be perfect). If you like a cleaner look, use a pizza cutter to cut off the rough edges. Otherwise, leave them as-is for a rustic look. Transfer the pie dough to the prepared sheet pan. Refrigerate the pie dough while you prepare the filling.

In a medium bowl, toss the pear slices with the lemon juice. Then, add the sugar, flour, ginger, cinnamon, and a pinch of salt. Toss well until the sugar dissolves.

Evenly spoon the pear filling in the middle of the pie dough, leaving a 2'' border. Leave as-is for a rustic look, or arrange the slices into a concentric circle for a pretty design. Fold the pie dough over the filling, overlapping the dough as needed. Gently press the folds to make sure they stick. Refrigerate the galette for 10-15 minutes.

Meanwhile, whisk the egg with 1 Tablespoon of water. Brush the egg wash on the edges of the chilled galette and sprinkle generously with Demerara sugar.

Bake the galette for 35-40 minutes until the filling is bubbly and the crust is deep golden-brown. Let it cool for 10-15 minutes before slicing. Serve warm with ice cream or whipped cream.