Preheat your oven to 350°F (175°C) and grease and flour your baking pan.
In a large mixing bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt until well combined.
In another bowl, mix together the egg, whole milk, vegetable oil, and vanilla extract until smooth.
Pour the wet mixture into the dry ingredients and stir gently. Gradually add warm water or brewed coffee while mixing until everything is combined.
Gently fold in the milk chocolate chips last.
Pour the batter into your prepared pan and bake for about 40 minutes or until a toothpick inserted into the center comes out clean.
Allow the cake to cool completely before frosting with sour cream mixed with vanilla extract.