1. Preheat oven to 350°F (175°C). Grease a 10×15-inch jelly roll pan or line with parchment paper.

2. In a large bowl, whisk together flour, sugar, salt, baking soda, and cinnamon.

3. In a saucepan, melt butter over medium heat. Add cocoa and water. Bring just to a boil, then remove from heat.

4. Pour the hot cocoa mixture into the dry ingredients and mix until just combined.

5. Add eggs, sour cream, and vanilla. Mix until smooth. Batter will be thin.

6. Pour batter into prepared pan. Bake for 18–22 minutes or until a toothpick inserted comes out clean.

7. While the cake bakes, make the frosting: melt butter in a saucepan, add cocoa and milk, and bring to a boil.

8. Remove from heat and whisk in powdered sugar and vanilla. Adjust consistency as needed.

9. Pour warm frosting over hot cake immediately. Spread evenly and sprinkle with pecans if using.

10. Let cool to room temperature before slicing and serving.