In a medium mixing bowl, whisk together flour, soda, salt and cream of tartar; set aside. With an electric mixer, beat butter and sugars until light and fluffy; scrape bowl. Add egg and vanilla; beat just until well combined. Add dry ingredients; beat on low speed just until flour is no longer visible. Mix in toffee bits. Chill dough for 1 hr. to no more than 1 ½ hrs. Scoop 19 evenly sized rounded spoonfuls (or use a #40 cookie scoop); roll in Cinnamon Sugar. Place cookies 2" apart on 2 parchment-lined baking sheets; bake in a preheated 350° oven until just barely set and slightly puffy (about 10 min.), rotating pans halfway through. Cool cookies on pans for 10 min.; move to wire racks to cool completely.

CINNAMON SUGAR: In a small mixing bowl, whisk together 1/4 cup sugar, 2 tsp. ground cinnamon and a pinch each of salt, ground cloves, ground nutmeg and ground allspice.