For the cake:

1. Preheat your oven to 350 degrees F.  Spray a sheet cake pan with cooking spray.
2. Place flour, sugar and salt in a large mixing bowl and whisk to combine.
3. In a small saucepan over medium high heat, melt butter.  Add water and cocoa powder.  Whisk to combine and bring to a boil, whisking frequently.
4. Remove from heat and pour over flour mixture.  Using a large spoon, stir well to combine.  Add buttermilk, vanilla and eggs.  Stir again to combine.
5. Pour batter into prepared sheet cake pan and bake for 25-30 minutes, or until a toothpick inserted in the middle is removed clean.
6. Using a skewer, poke holes about 1-inch apart throughout the cake and prepare frosting.

For the frosting: 

1. Pour powdered sugar in a large mixing bowl.
2. In a small saucepan over medium high heat, melt butter.  Add cocoa powder and milk and whisk to combine.  Bring to a boil, whisking constantly.
3. Pour mixture over powdered sugar and add vanilla extract.  Stir with a large spoon until smooth.  Add more milk if needed for desired consistency.
4. Spread warm frosting evenly over cake and sprinkle evenly with toasted chopped pecans.