Preheat oven to 350 degrees. Line a 10 x 15 baking sheet with parchment. Mix flour, baking soda and salt together. In a mixing bowl, beat butter, shortening, and sugars. Add vanilla and eggs. Mix well. Add flour mixture and mix until all of the dry ingredients are well incorporated. Stir in the candy bar pieces. Spread in prepared baking pan. Bake 20 - 25 minutes, until golden brown. Cool 10 minutes. With a two inch heart-shaped cookie cutter cut out hearts. (reserve the remaining bits left in the pan after cutting out the hearts, use to crumble on top of ice cream or just to snack on!)