In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.

Add the egg and vanilla extract to the butter-sugar mixture and mix well until fully combined.

In a separate bowl, whisk together the all-purpose flour and salt.

Gradually add the dry ingredients to the wet ingredients, mixing until a dough forms. If the dough feels too sticky, you can add a little more flour.

Divide the dough into two equal portions. Wrap each portion in plastic wrap and refrigerate for about 20 minutes to firm up.

Take one portion of the dough out of the refrigerator. On a lightly floured surface, roll it out to about ¼ inch thickness.

Use cookie cutters of your choice to cut out shapes from the rolled dough. Make sure to leave a hollow space in the center of each shape where the "stained glass" will go.

Carefully transfer the cut-out shapes to the prepared baking sheets, leaving some space between them.

Take the crushed hard candy and fill the hollow centers of the cookie shapes with the candy. You can use one color per cookie or create patterns with multiple colors.

Repeat steps 7-10 with the second portion of dough.

Place the baking sheets with the cookies in the preheated oven and bake for 10-12 minutes or until the edges of the cookies are lightly golden brown and the candy has melted and filled the hollow centers.

Remove the baking sheets from the oven and allow the cookies to cool on the sheets for a few minutes. Then transfer them to a wire rack to cool completely.

Repeat the baking process with any remaining dough.