Preheat oven to 375°F. Line several cookie sheets with parchment paper.
Beat butter, granulated sugar, brown sugar, vanilla and salt in large bowl until blended. Add eggs; beat well. Stir together flour, baking soda and cream of tartar; gradually add to butter mixture, beating until blended. Stir in toffee bits. Drop 1 tbsp of batter for each cookie onto prepared cookie sheet.
Bake 8 to 10 minutes or until lightly browned. Cool slightly; remove to wire rack. Cool completely. Makes about 6 dozen cookies.
**Hershey's original recipe says 350 for 8-10 minutes, with each cookie a heaping tsp of dough. That gave me underbaked cookies.