Preheat your oven to 175°C (350°F) and grease a 9x13-inch baking pan with cooking spray.
In a mixing bowl, combine the flour, sugar, baking soda, salt, and cocoa powder. Whisk until well combined.
Add the oil, boiling water, buttermilk, eggs, and vanilla extract. Beat until well mixed.
Pour the batter into the prepared pan and spread it evenly.
Bake for about 45 minutes or until a toothpick inserted into the center of the cake comes out clean.
In a saucepan, combine the milk, butter, corn syrup, and sugar. Stir until well mixed and bring the mixture to a boil for at least 2 minutes.
Add the chocolate chips, vanilla extract, and nuts (if using). Stir until the chocolate chips are melted.