Preheat your oven to 350°F (175°C). Grease two 9-inches round cake pans and lightly sprinkle them with flour, or line them with parchment paper to prevent sticking.

In a large bowl, combine 2 ⅓ cups of all-purpose flour, 2 ¼ teaspoons of baking powder, and ¼ teaspoon of salt. Stir them together and set the bowl aside.

In a separate bowl, whisk 1 ½ cups of sugar, ¾ cup of vegetable oil, and 3 large eggs until the mixture is smooth. Add 1 tablespoon of vanilla extract and ¾ cup of whole milk, and then mix until fully combined.

Slowly add the dry ingredients to the wet mixture, stirring gently. Mix just until everything is combined over mixing can make the cake dense.

Divide the batter evenly between the two prepared pans. Bake for 30–35 minutes, or until a toothpick inserted in the center comes out clean. Let the cakes cool in the pans for about 10 minutes, and then transfer them to a wire rack to cool completely.

In a medium bowl, combine ⅔ cup of unsweetened cocoa powder with ½ cup of melted butter. Add ⅓ cup of milk and 1 teaspoon of vanilla extract. Gradually whisk in 3 cups of confectioners’ sugar until smooth and creamy. If the frosting is too thick, add a little more milk until it reaches the desired consistency.

Once the cakes are completely cooled, place one layer on a serving plate. Spread a generous amount of chocolate frosting on top. Place the second layer over it, and then frost the top and sides of the cake evenly with the remaining frosting.

Slice the cake and serve at room temperature. Store any leftovers in an airtight container at room temperature for up to three days.