Preheat your oven to 350°F (175°C). Grease a 13×18-inch rimmed baking sheet or line it with parchment paper.

In a large bowl, whisk together flour, sugar, baking soda, and salt until well combined.

In a separate bowl, beat eggs, then stir in buttermilk, melted butter, and vanilla extract.

Pour wet ingredients into dry ingredients and stir until smooth—no lumps!

Spread batter evenly on your prepared sheet pan. Bake for 18–20 minutes, or until a toothpick inserted comes out clean.

While the cake bakes, melt together ½ cup butter, ¼ cup cocoa powder, and ⅓ cup milk in a saucepan over medium heat. Bring to a gentle boil, then remove from heat and whisk in 2 cups powdered sugar and 1 tsp vanilla until smooth.

As soon as the cake is out of the oven, pour the warm chocolate icing over the top. Use a spatula to spread evenly—and sprinkle chopped walnuts for that classic texas crunch.

Let the cake cool for at least 15 minutes before slicing. Cut into squares and serve.