1. In a medium mixing bowl, whisk together flour, baking soda, salt and cream of tartar; set flour mixture aside.
2. In a large mixing bowl, beat butter and sugars with an electric mixer until light and fluffy; scrape bowl.
3. Add egg and vanilla; beat just until well combined.
4. Add flour mixture; beat on low speed just until flour is no longer visible.
5. Stir in toffee bits.
6. Chill dough in the refrigerator for 1 hr. to no more than 1 ½ hrs.
7. Preheat oven to 350°.
8. Scoop chilled dough into 19 evenly sized rounded spoonfuls (or use a #40 cookie scoop); roll in cinnamon sugar. Place dough balls 2" apart on 2 parchment-lined baking sheets.
9. Bake in preheated oven until cookies are just barely set and slightly puffy (about 10 min.), rotating pans halfway through.
10. Remove from oven; let cookies cool on pans for 10 min.
11. Transfer cookies to wire racks to cool completely.

CINNAMON SUGAR: In a small mixing bowl, whisk together ¼ cup sugar, 2 tsp. ground cinnamon and a pinch each of salt, ground cloves, ground nutmeg and ground allspice. Makes about ¼ cup.