Preheat the oven to 350°F (175°C). Lightly grease a baking dish and set aside.
In a large mixing bowl, whisk together the flour, cocoa powder, sugar, baking powder, and salt until evenly combined. The mixture should look uniform and slightly powdery.
1 1/2 cups all-purpose flour, 1 cup granulated sugar, 1/2 cup unsweetened cocoa powder unsweetened cocoa powder, 1 teaspoon baking powder baking powder, 1/2 teaspoon salt salt
In a separate bowl, whisk together the eggs, vegetable oil, vanilla extract, and buttermilk until smooth and slightly frothy. The mixture should appear well combined with no streaks of eggs.
2 large eggs eggs, 1/2 cup vegetable oil vegetable oil, 1 teaspoon vanilla extract vanilla extract, 3/4 cup buttermilk buttermilk
Pour the wet mixture into the bowl of dry ingredients. Using a spatula or whisk, gently fold them together until just combined; do not overmix. The batter will be thick and smooth.
1/2 cup vegetable oil vegetable oil, 2 large eggs eggs, 1 teaspoon vanilla extract vanilla extract, 3/4 cup buttermilk buttermilk
If using chocolate chips, fold them into the batter now. Transfer the batter into the prepared baking dish, spreading evenly with a spatula.
Optional chocolate chips or chunks
Bake in the preheated oven for about 35 minutes, or until the top is set and feels slightly firm to the touch. A toothpick inserted into the center should come out with moist crumbs but no wet batter.
Remove the cake from the oven and place on a cooling rack. Allow to cool for at least 20 minutes before slicing. The surface should have a slight sheen and the edges slightly pull away from the sides of the dish.
