Step 1: Prepare the Cookie Dough: In a large bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy. This process incorporates air, resulting in a tender cookie dough.
Step 2: Incorporate Wet Ingredients into the Cookie Dough: Beat in the eggs one at a time, then stir in the vanilla extract. Ensure each egg is fully incorporated before adding the next. This helps to create a smooth, even dough.
Step 3: Combine Dry Ingredients into the Cookie Dough: In a separate bowl, whisk together the flour, baking soda, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Be careful not to overmix, as this can lead to a tough dough.
Step 4: Add Chocolate Chips to Cookie Dough: Stir in the chocolate chips until evenly distributed throughout the dough. This can be done by hand or with a mixer on low speed.
Step 5: Prepare Cake Batter: Preheat oven to 180C (350F). Grease and flour a 9-inch round cake pan. In a large bowl, cream together the softened butter and sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla extract.
Step 6: Combine Dry and Wet Ingredients for Cake: In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add the dry ingredients to the wet ingredients, alternating with the milk, beginning and ending with the dry ingredients. Mix until just combined.
Step 7: Assemble the Cake: Pour half of the cake batter into the prepared cake pan. Drop spoonfuls of the cookie dough evenly over the cake batter. Pour the remaining cake batter over the cookie dough, spreading it evenly.
Step 8: Bake the Cake: Bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean. If the top starts to brown too quickly, cover it loosely with aluminum foil.
Step 9: Cool the Cake: Let the cake cool in the pan for 10 minutes before inverting it onto a wire rack to cool completely. This prevents the cake from sticking to the pan.
Optional Tip: For a richer flavor, substitute dark chocolate chips for milk chocolate chips. Alternatively, add a teaspoon of espresso powder to the cake batter for a mocha-flavored twist.