Heat butter in a large saucepan over medium heat until golden brown, about 7-9 minutes (do not burn). Remove from the heat; stir in brown sugar until blended., Transfer to a large bowl, cool slightly. Whisk in eggs, 1 at a time. Combine the flour, cream of tartar, baking soda and salt; gradually add to butter mixture and mix well. Stir in pecans., Shape dough into four 8-in. rolls; wrap each in waxed paper. Refrigerate for 8 hours or overnight., Unwrap rolls and cut into 1/4-in. slices. Place 2 in. apart on ungreased baking sheets. Bake at 375° just until set, 5-7 minutes. Cool for 1 minute before removing from pans to wire racks.