Begin by preparing your ingredients and workspace. Sift together 1 cup of cake flour, 1 teaspoon of baking powder, and 1/2 teaspoon of salt in a medium bowl. This indispensable step aerates the dry ingredients and helps distribute the leavening agent evenly throughout the mixture.
In a separate bowl, combine your wet ingredients: 4 ounces of melted chocolate, 1 cup of skim milk, 4 eggs, 1 cup of sugar, and 1 teaspoon of vanilla. Blend these wet ingredients together until well combined and smooth. Gently fold the dry mixture into the wet ingredients, stirring carefully to avoid deflating any air that may have been incorporated into the eggs.
Pour the batter into a prepared 8-inch baking pan, spreading it evenly across the bottom. Bake at 350 degrees Fahrenheit for 20 to 30 minutes, watching carefully until the cake turns golden brown and a toothpick inserted in the center comes out clean.
The exact baking time may vary slightly depending on your oven's characteristics, so begin checking around the 20-minute mark. Once the cake has achieved that golden exterior and is set in the center, remove it from the oven and allow it to cool completely in the pan before turning it out onto a wire rack or serving plate.