Preheat oven to 350°F. Grease or line a 9x13-inch baking dish with parchment paper.

In a saucepan, heat Coca-Cola, butter, oil, and cocoa over medium heat until melted and just starting to bubble. Remove from heat.

In a large bowl, whisk together flour, granulated sugar, brown sugar, baking soda, salt, and espresso powder.

In a separate bowl, whisk together buttermilk, eggs, and vanilla extract.

Pour the wet ingredients into the dry ingredients and stir gently just until smooth with a wooden spoon or rubber spatula.

Pour batter into prepared pan and bake for 30–35 minutes or until a toothpick inserted in the center comes out with moist crumbs.

While the cake is baking, prepare the glaze. In a small saucepan, combine butter, Coca-Cola, and cocoa powder. Bring to a gentle bubble, then remove from heat.

Whisk in powdered sugar and salt until smooth.

Pour glaze over the warm cake, and tilt the pan to spread it evenly. Optional: top with chopped pecans or walnuts.

Let glaze set for 30–45 minutes before slicing.