Bavarian Plum Tart (Zwetschgendatschi)

Beat butter in large bowl until smooth; continuing to beat, add sugar gradually until mixture is light and fluffy; beat in egg, vanilla, and salt until thoroughly blended. Sift flour and baking powder together into separate bowl. Gradually stir flour mixture into butter mixture until a soft, but not sticky, dough forms. Add more flour, 1 tablespoon at a time, if necessary, to eliminate stickiness. Refrigerate dough, wrapped in aluminum foil, until chilled, about 30 minutes.

Meanwhile, quarter plums lengthwise, removing pits; reserve plums at room temperature.

Butter 15.5"x10.5"x1" baking pan. Dust with flour; shake out excess.

Using rolling pin covered with lightly floured stockinet, roll chilled fough out on lightly floured pasty cloth to approximate size of baking pan. Carefully roll up pastry on rolling pin and transfer to prepared pan. Press pastry along bottom and 1/2 inch up sides of pan with lightly floured fingers; if pastry tears, press with fingers to seal. Refrigerate pastry-lined pan until pastry is well chilled, at least 30 minutes.

Heat oven to 400F.

Arrange plum quarters, cut side up and overlapping, in rows on chilled pastry. Bake tart until crust is golden brown, about 25 minutes; cool in pan on wire rack.

At serving time, sift confectioner's sugar generously over top of tart. Serve with whipped cream, if desired.