Step #1 In a big bowl, beat butter with an electric mixer on medium to high speed for 30 seconds.
Step #2 Add in sugar; beat until mixd.
Step #3 Beat in egg yolks, milk, & mint extract until mixd.
Step #4 Beat in as much of the flour as you can with the mixer; stir in the any remaining flour with a wooden spoon; cover & chill dough about 2 hrs or until easy to handle.
Step #5 Shape dough into 1-inch balls; place on ungreased cookie sheet.
Step #6 If desired, flatten cookies with the decorative bottom of a glass dipped in colored sugar.
Step #7 Bake at 350° for 8-10 mins or until edges begin to brown; transfer cookies to a wire rack & let cool.