Chocolate Cake with Chocolate-Pecan Frosting

Ingredients

• all-purpose flour
  2 cups
• granulated sugar
  2 cups
• baking soda
  1 teaspoon
• of salt
  1 Pinch
• (1 stick) unsalted butter

  cut up
  8 tablespoons
• (1 stick) margarine

  cut up
  8 tablespoons
• water
  1 cup
• unsweetened cocoa powder (not Dutch process)
  1/3 cup
• sour cream
  3/4 cup
• eggs
  2 large
• vanilla extract
  1 teaspoon
• Frosting
  1 unit
• (1 stick) unsalted butter

  cut up
  8 tablespoons
• plus 1 tablespoon milk
  1/3 cup
• unsweetened cocoa powder (not Dutch process)
  1/4 cup
• (about 4 1/3 cups) confectioners' Sugar

  sifted
  1 pound
• vanilla extract
  1 teaspoon
• (4 ounces) coarsely chopped pecans

  toasted
  1 cup