Combine flour, sugar and salt. Cut in butter cubes and grated orange zest until mixture resembles a coarse meal. Add beaten egg and mix until evenly combined. Add orange juice a teaspoon at a time; add just enough so that the dough will adhere together when pressed.
Form dough into 4 flattened disks, wrap in plastic wrap and refrigerate 2 to 3 hours or overnight.
Preheat oven to 375°F.
On a lightly floured surface or between sheets of parchment paper, roll chilled dough disks to a thickness of 1/8 inch. Cut out dough with a 2-inch fluted edge round cookie cutter, then cut a ½-inch hole in the center of half of the cookies (an apple corer works well). Keep dough chilled for ease of handling, returning it to the refrigerator if it seems sticky.
Bake cookies on an ungreased cookie sheet for about 10 minutes or until lightly browned at the edges.
Let cookies cool, then spread apricot jam on the bottoms of the solid cookies and sift powdered sugar over the tops of the cookies with holes.
Place sugar sprinkled cookie on top of jam-coated cookie to form sandwich; jam peeks through to form the ‘blossom’ center.