In a microwave-safe mug, whisk together the flour, cocoa powder, sugar, baking powder and salt.
Add the milk, melted butter, and vanilla extract. Stir until smooth.
Gently fold in the raspberries and chocolate chips (if using).
Microwave on high for 60-90 seconds, until the cake has risen and is set in the center. Cooking time may vary based on your microwave. Start with 60 seconds and increase cooking time from then.
Let cool for a minute before digging in. Enjoy warm!