Follow the steps in order for the best result.
Begin by preheating your oven to 350°F (175°C).
In a spacious mixing bowl, combine the cake flour, baking soda, and salt. Sift these ingredients together to ensure they are well incorporated. Set the bowl aside.
In a separate bowl, preferably using an electric mixer, cream together the softened butter and sugar until the mixture becomes light and fluffy. This may take a few minutes.
Incorporate the cooled, melted chocolate and vanilla extract into the butter-sugar mixture. Beat for approximately 3 minutes until everything is thoroughly combined.
Add the eggs one at a time, beating well after each addition. Scrape down the sides of the bowl to ensure even mixing, and then beat for an additional 3 minutes.
Gradually introduce the dry ingredients (flour, baking soda, salt) into the wet ingredients in three separate additions. Alternate each addition with the warm water, mixing for about 1 minute after each addition to ensure the ingredients are well combined.
Line a baking sheet with parchment paper. Pour the batter onto the prepared sheet and use a spatula to spread it evenly.
Bake in the preheated oven for approximately 20 minutes, or until a cake tester inserted into the center comes out clean. This indicates that the cake is fully baked.
Allow the cake to cool completely before proceeding with the next steps.