1. With an electric mixer, beat butter, sugar, egg, and vanilla 3 to 4 minutes, until light and fluffy. Add flour and salt and continue beating 2 minutes more, until well blended.
2. Roll dough into a 2-inch-thick log. Wrap in plastic and chill 30 minutes.
3. Heat oven to 350 degrees F. Line two baking sheets with aluminum foil. Cut dough into 1/4-inch-thick slices and place on sheets 3 inches apart. Cut out heart shapes from centers of slices with cookie cutters in assorted sizes. Place heart-shaped cutouts alongside larger cookies. Bake 10 minutes.
4. Take baking sheets out of the oven and remove small cookies; fill large cookie centers with crushed candy; bake 1 to 2 minutes more, or until candy melts. Cool on baking sheets 5 minutes. Transfer to wire rack to cool completely. Repeat with remaining dough and candy.