1 1/4 cups (6 1/4 ounces) all purpose flour
1 2/3 cups (12 1/4 ounces) sugar
2/3 cup cocoa powder
1/2 teaspoon salt
1/2 teaspoon baking powder
1 can (12 ounces) Coca Cola
Adjust oven rack to middle position and preheat oven to 350°F. Either grease baking pan with oil or cover with tin foil.
In a large bowl, stir together flour, sugar, cocoa, salt, and baking powder until combined. Add cola, a little at a time because it will foam, until incorporated and batter forms. Pour batter into 9- by 13-inch pan and bake until a tester inserted into the middle of the pan comes out clean, about 30 minutes. Top will be slightly sticky.
Let cool completely in pan then cut into squares.