•  1 1/3 cups (6.75 ounces) all-purpose flour
  •  1 cup (7.5 ounces) granulated sugar
  •  1 cup (7.5 ounces) brown sugar
  •  1/2 cup (1.5 ounces) unsweetened cocoa powder
  •  1/2 teaspoon baking soda
  •  1/2 teaspoon salt
  •  1 cup (8 ounces, 16 tablespoons) butter, melted
  •  4 large eggs
  •  1 teaspoon vanilla extract
  •  10-ounce package mini marshmallows (4-5 cups)
  •  1 cup (about 4 ounces) chopped pecans, toasted (optional but delicious)
  •  1/3 cup (about 1 ounce) unsweetened cocoa powder
  •  1/4 cup milk
  •  1/4 cup (2 ounces, 4 tablespoons) butter
  •  Pinch of salt
  •  2 cups (8 ounces) powdered sugar
  •  1 teaspoon vanilla extract
  1. Preheat the oven to 350 degrees F. Line a large, rimmed baking sheet (half sheet pan, about 12X18 inches) with parchment and lightly grease with cooking spray. Alternately, you can line with foil and grease the foil or leave the pan unlined and grease the pan.
  2. For the bars, in a large bowl, whisk together the flour, sugar, brown sugar, cocoa (sift the cocoa into the bowl using a fine mesh strainer if it is overly clumpy), baking soda and salt. Add the melted butter, eggs, and vanilla. Mix together until combined (don't overmix; just whisk/stir until no dry streaks remain and ingredients are evenly combined).
  3. Spread the batter evenly in a thin layer in the prepared pan. Bake for 15-20 minutes until the top is springy to the touch and a toothpick inserted in the center comes out clean. Watch closely so the thin bars don't overbake!
for full instructions you can go to :    https://www.melskitchencafe.com