Preheat oven to 375°.
Lightly spoon flour into a dry measuring cup; level with a knife. Combine granulated sugar and cinnamon; stir well.
Place egg whites, cream of tartar, and salt in a large bowl; beat with a mixer at high speed until foamy. Gradually add cinnamon- sugar mixture, beating until stiff peaks form. Sift 1/4 cup flour over egg white mixture; fold in. Repeat procedure with remaining flour, 1/4 cup at a time. Combine pecans, toffee bits, and brown sugar; stir well. Gently fold pecan mixture and vanilla into egg white mixture.
Spoon batter into an ungreased 10-inch tube pan, spreading evenly. Break air pockets by cutting through batter with a knife. Bake at 375° for 40 minutes or until cake springs back when lightly touched. Invert tube pan onto a heatproof glass bottle, and cool completely upside down in pan. Loosen cake from sides of pan using a narrow metal spatula. Invert angel food cake onto a serving platter.
Note: This cake may brown nicely and test done before 40 minutes, but the sticky nature of the toffee bits and sugar make it necessary to bake the cake for the full amount of time.