Toast nuts at 400 degrees F for 10 minutes and chop very fine. Mix together flour, sugar, cinnamon, baking powder, and nuts. Cut in butter and moisten dough with egg, adding only enough to make a pliable but not sticky dough. Wrap in plastic wrap and chill until firm, at least 1 hour. Roll two-thirds of the dough on a flour-covered cloth and line a 9-inch tart pan with removable bottom. Press well into bottom. Spread dough with preserves to within 1 inch of the edge. Roll remaining dough and cut into thin strips. Make a lattice by laying 5 strips (about ½-inch wide) each way. Roll scraps of dough into small ½-inch balls and place them all around inside edge of pan. Bake at 375 degrees F for 30 minutes (don’t let preserves boil). Cool on rack and sprinkle with confectioners’ sugar.