• If making the grapefruit cookies, add the zest to the butter and sugar before beating.
• Beat the butter and sugar together until white in color...about 6 minutes. Beat in the vanilla, if using.
• Beat in the flour just until combined. Press the dough into a ball. If the dough is too dry and not coming together, add a tablespoon of milk or water (repeating as necessary) until you can shape it into a ball.
• Put the dough into the fridge to chill for about 1 hour.
• On lightly floured surface, roll the dough out to 1/2 inch thickness. Use a cutter to cut 2 inch diameter circles.

  OR, roll the dough into a log about 2 inches in diameter. Slice 1/2 inch thick slices.
• At 350 degrees, on an ungreased cookie sheet, bake the cookies for about 8-10 minutes. --do NOT overbake. Do not let these cookies get golden brown.

for the icing...

• Put the juice into the mixing bowl and add about 1 cup of powdered sugar, beat well. Add the zest. And then slowly add in the additional powdered sugar. Continue beating until well combined. If needed, add powdered sugar or juice. 
• Dip the tops of the cooled cookies into the icing and set parchment paper or rack. Let the icing dry and harden for about 15 minutes. Wait a couple of hours before stacking them.