Stepwise Method:

• Step 1: Preheat and Prepare - Preheat your oven to 350°F (175°C). Grease your 9-inch round cake pan with butter or cooking spray, and lightly dust with flour, or line it with parchment paper for easy removal.
• Step 2: Combine Dry Ingredients - In a medium bowl, whisk together 1-1/2 cups of all-purpose flour, 1 teaspoon of baking soda, and 1 teaspoon of baking powder. Set aside.
• Step 3: Cream Butters and Sugars - In a large mixing bowl, use an electric mixer to beat 1 cup of unsalted butter and 1 cup of packed dark brown sugar together until smooth and creamy. Then, add 1 cup of granulated sugar and continue mixing until well combined.
• Step 4: Add Egg and Vanilla - Add 1 large egg and 1 teaspoon of vanilla extract to the butter and sugar mixture. Beat until everything is fully incorporated.
• Step 5: Mix Dry Ingredients - Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix.
• Step 6: Fold in Chocolate Chips - Using a spatula, gently fold in 1 cup of semi-sweet chocolate chips until evenly distributed throughout the batter.
• Step 7: Bake the Cake - Pour the batter into the prepared cake pan, spreading it evenly. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean. Let the cake cool in the pan for about 10 minutes before transferring it to a cooling rack to cool completely.
• Step 8: Make the Frosting - In a medium bowl, beat 4 tablespoons of salted butter until creamy. Add 2 tablespoons of unsweetened cocoa powder, 1-1/4 cups of powdered sugar, and 2 tablespoons of whole milk. Mix until smooth and fluffy. Adjust the consistency with more milk or powdered sugar as needed.
• Step 9: Frost the Cake - Once the cake is completely cool, spread the chocolate frosting evenly over the top. Don’t be shy—make it thick and luscious!
• Step 10: Add Sprinkles - Finish off your masterpiece with a generous sprinkle of colorful sprinkles on top for that festive touch.