Mix flour with sugar, salt, cream of tartar, soda and cinnamon. Cream butter to soften. Add four mixture, milk and vanilla. Mix until all flour is moistened, then beat 2 minutes at medium speed. Add eggs and chocolate. Beat 1 minute more. Pour into prepared pan (bundt or tube). Bake 1 hour and 20 minutes at 160ºC or until cake tester comes out clean. Cool in pan 15 minutes. Remove and complete cooling on rack. Glaze. Glaze: Melt semi sweet chocolate with butter, stirring constantly. Cool slightly and drizzle with tip of spoon over top of cake. ----