Cream butter and sugar with electric mixer until light and creamy colored, about 5 minutes. Add eggs, beating well after each.
Mix flour, cocoa, salt and cinnamon together in a medium bowl. Gradually add flour mixture and water to batter, alternating. Beat in vanilla extract. Combine soda and hot water in a small bowl; fold into batter. Portion into cupcake pans lined with liners.
Bake for 20 to 25 minutes at 350º F. Cool at least 30 minutes
Beat all frosting ingredients together in a large bowl until creamy. Ice each cupcake.