Coat a baking sheet lightly with no-stick cooking spray.
Combine brown sugar, granulated sugar, evaporated milk and corn syrup in 3-quart saucepan. Heat to boiling over medium heat, stirring constantly. Cover and boil 1 minute. Uncover. Cook over medium heat, without stirring, to 235 degrees F on candy thermometer. Remove from heat.
Add shortening, vanilla, pecans and cream of tartar. Stir with wooden spoon until mixture thickens slightly. Do not overstir. Let the mixture stand 3 minutes. Drop by rounded tablespoonfuls onto prepared baking sheet. Cool until firm.