In a microwave-safe mug (10-12 oz), mix together the milk and oil using a fork.
Add the sugar and mix well.
Sift in the dry ingredients (flour, cocoa powder, baking powder, and salt), then gently stir with the fork. Make sure to scrape the edges to mix everything thoroughly.
Stir in the chocolate chips.
Clean the edges of the mug if needed, then microwave for about 60-90 seconds.
Spread some Nutella on top and enjoy!
Notes
To measure flour accurately, fluff it up with a fork first, then add it to the tablespoon measure, wiping off any excess flour from the top.