1) To make the pastry: Whisk together the flour, salt and baking powder.
2) Cut the cold butter into pats and work it into the flour mixture with your fingers or a pastry blender. The mix will be crumbly, with some larger piece of butter about the size of raisins still visible.
3) Stir in the sour cream, then turn the mixture out onto the work surface and bring together with a few quick kneads. The dough will feel a bit rough.
4) Gently roll the dough to an 8" x 10" rectangle on a lightly floured surface. Turn the dough over so both sides are lightly floured.
5) Fold the dough in thirds as you would a business letter. Turn the dough over so the seam is down, and rotate until the short sides are at the top and bottom again.
6) Repeat the rolling and folding once more. Wrap well in plastic wrap and chill for at least 30 minutes or up to overnight. Prepare either a 9" round pie pan, or four 6" round pie pans with cooking spray.
7) While the dough is chilling you can cook the filling. Place the raisins and diced ginger in a large, heavy bottomed sauce pan. Add water just to cover and simmer over medium low heat until all the water is evaporated but the fruit is still moist.
8) Add the diced pears, sugar, lemon juice, butter, spices, and thickener to the pot and continue to cook over medium-low heat for 15 minutes until the pears have softened, but still retain their shape. Allow the mixture to cool to lukewarm.
9) Preheat the oven to 375°F . Pour the ginger-pear filling into your chosen pan(s). Roll half of the chilled pastry to a sheet 1/4" thick. Cut a round piece of pastry 1" smaller than the top of your pie pan and place it over the filling. You should be able to see filling all around the pastry, like water around an island. (Reserve the second half of the pastry for another use).
10) Brush the top of the pastry with lightly beaten egg, egg white, or milk and sprinkle on coarse sugar if desired. Bake small pies for 20 to 25 minutes, large pies for 30 to 35 minutes or until the filling is bubbling and the pastry is golden brown and flaky. Serve warm with freshly whipped cream. Makes one 9" pie or four 6" pies.