Heat chocolate over hot water until partially melted. Remove from heat and stir rapidly until melted. Cool.

Sift flour with sugar, salt, cream of tartar, baking soda, and cinnamon.

Stir melted cooled chocolate into shortening; add flour mixture, milk, and vanilla. Mix until all flour is dampened. Beat 2 minutes at medium speed of electric mixer or 300 vigorous strokes by hand.

Pour into a 9 or 10 inch tube pan that has been greased and floured on sides and tube and lined on the bottom with wax paper.

Bake in preheated oven about 1 hour and 5 to 10 minutes. Cool in pan 15 minutes and then remove to wire rack.