Preheat the oven to 175°C (350°F) and prepare a cake pan.
Mix flour, sugar, baking powder, and salt in a bowl.
Add butter, eggs, milk, and vanilla extract, then mix until smooth.
Pour the batter into the pan and bake for 30–35 minutes.
Allow the cake to cool completely.
Prepare chocolate frosting by mixing butter, cocoa, sugar, and milk until creamy.
Spread chocolate frosting over the cake and serve.