ingredients

    1/2 cup (1 stick or 4 ounces) unsalted butter, softened
    1 cup (6 7/8 ounces) firmly packed light brown sugar
    1/2 cup (4 ounces) granulated sugar
    1 large egg, at room temperature
    1 cup buttermilk
    1 teaspoon vanilla extract
    1 1/2 cups (6 3/4 ounces) all-purpose flour
    3/4 cup (2 5/8 ounces) Dutch cocoa powder
    1/4 teaspoon baking soda
    1/2 teaspoon baking powder
    1/4 teaspoon salt

Source: http://www.tastebook.com/recipes/2743407-Everyday-Chocolate-Cake