Combine 1/2 cup milk with 2 tablespoons cocoa, 1/2 cup sugar, butter, and oil in a saucepan over low heat. Stir continuously with a hand whisk until fully melted and smooth. Remove from heat and let cool completely.

Mix the flour with 1/2 teaspoon baking powder and add gradually to the mixture, beating well.

Pour the batter into a buttered and floured baking pan.

Add chocolate pieces of your choice, such as chocolate chips, Mars, or Galaxy, into the batter.

To make the sauce, place 1/4 cup milk, a piece of butter, 2 tablespoons cocoa, and 2 tablespoons sugar (or more to taste) in a saucepan over heat. Stir until thickened, then let cool.