Preheat oven to 375°.
To prepare cookies, place granulated sugar and butter in a large bowl; beat with a mixer at medium speed 3 minutes or until light and fluffy. Beat in rind and 1/4 cup juice. Add eggs, 1 at a time, beating well after each addition (mixture will look curdled).
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, baking powder, and salt, stirring well with a whisk. Add flour mixture to sugar mixture; stir with a wooden spoon to form a stiff dough. Turn dough out onto a floured surface; knead 10 to 15 times to form a smooth dough.
Divide dough into 8 equal portions. Working with 1 portion at a time (cover remaining dough to prevent drying), shape each portion into a 30-inch-long rope; cut each rope crosswise into 6 (5-inch) pieces. Tie each dough piece into a knot. Place knots on 2 baking sheets coated with cooking spray. Bake 1 sheet at a time at 375° for 8 minutes or until bottoms of cookies are lightly browned and tops are still pale. Remove cookies from pan; cool on wire racks.
To prepare glaze, combine powdered sugar, 3 tablespoons juice, and buttermilk; stir until smooth. Dip tops of cookies into glaze; dry on racks.