Cookies

1 cup plus 2 tablespoons (2 ¼ sticks) butter

2 1/4 cups (1 pound) sugar

2 eggs

2 teaspoons vanilla extract

2 3/4 cups plus 1 tablespoon (12 ounces) flour

1/2 cup plus 2 tablespoons (2.4 ounces) cocoa powder

1 teaspoon baking soda

1 teaspoon salt

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Filling and assembly

1 1/4 cups (21/2 sticks) butter

6 cups powdered sugar

2 1/2 teaspoons vanilla extract

1 tablespoon plus ¾ teaspoon water

1 1/4 teaspoon salt

Cooled cookies