In a large bowl, combine butter, powdered sugar and ½ teaspoon peppermint extract. Beat until creamy, scraping down sides of bowl. Add flour and cornstarch; beat on low until well mixed. Cover and refrigerate until firm, about 60 minutes.
Shape rounded tbs of dough into 1-inch balls. Place 1-2 inches apart onto ungreased cookie sheet. Bake @ 350 for 12-15 minutes or until edges are lightly browned. Let cool on cookie sheet for 1 minute then remove to cooling rack to cool completely.
For glaze, in a small bowl, combine 1½ cups powdered sugar, 2 TB butter, ¼ tsp peppermint extract and milk (enough to reach desired consistency). Mix in for coloring. Drizzle over cooled cookies and sprinkle with crushed candy.