In a large bowl, cream together the butter and sugar with an electric mixer on medium speed.
Add the eggs, vanilla and salt and continue blending until thoroughly combined.
Slowly add the flour, mixing just until combined. DO NOT OVERMIX.
Cover the dough and chill in the refrigerator for one hour.
While the dough is chilling, preheat the oven to 350 degrees. Line a baking sheet with a silicon baking mat (preferred) or parchment paper.
Remove dough from the refrigerator and roll out onto a floured surface about a half of an inch thick.
Cut Into desired shapes, being sure to cut out hollow areas to place candy.
Place shapes onto the prepared baking sheet.
Unwrap the hard candies and place into separate plastic bags by color (don't mix the colors in one bag).Cover the bag with a kitchen towel and break into small pieces using a rolling pin or other heavy tool. DO NOT crush the candies into a powder.
Place the candy pieces in the hollowed out areas of the cookies.
Bake for 10-12 minutes or until the cookies are set and the candy centers are melted.
Allow to cool on the baking sheet until the candy 'glass' has completely cooled.
OPTIONAL: Glazing the cookies. Combine the powdered sugar and just enough milk to allow the glaze to be drizzled. Drizzle over the cooled cookies and allow to set.