Finely grind the almonds and flour in a food processor. Mix in the sugar, butter, blending until smooth. Mix in the egg. Transfer filling to medium bowl. Cover and chill at least 3 hours. (Can be made 2 days ahead. Keep chilled.)
Position rack in center of oven and preheat oven to 375°F. Roll out chilled dough on a lightly floured sheet of parchment paper or lightly floured work surface. Turn dough into 9" diameter tart pan with removable bottom or 9" pie plate. Seal any cracks in dough. Trim overhang if needed. Pierce crust all over with fork. Freeze the crust for about 10 minutes.
Line the crust with buttered foil, buttered side down, then fill with dried beans or pie weights. Bake crust until sides are set, for about 20 minutes. Remove foil and beans. Bake crust until sides are golden and bottom is set, pressing with back of fork if crust bubbles, for about 10 minutes longer. Cool crust in pan on rack. Reduce oven temperature to 350°F.
Spread almond filling evenly in crust. Stem pears and cut each in half lengthwise; scoop out cores. Cut each half crosswise into thin slices. Gently press each pear half to fan slices but keep slices tightly overlapped. Slide spatula under pears and arrange on top of the filling.
Bake tart until golden and tester inserted into the center of filling comes out clean, for about 55 minutes. Cool tart in pan on rack. Sprinkle with powdered sugar, if desired, and serve.