Preheat oven to 350 degrees F. Butter a 12-inch cast iron skillet or 9 x 13-inch baking pan.

In a large bowl combine the sugar, flour, cocoa powder, cinnamon and salt. Mix in the eggs and butter.

Pour the batter into the skillet or pan. Bake for about 25 to 30 minutes or until a toothpick comes out clean.