In a small microwave-safe bowl, whisk together granulated sugar, cocoa powder, water, oil, brown sugar, vanilla extract, and a pinch of salt until smooth.
Add the all-purpose flour and stir until just combined, being careful not to overmix.
Fold in the semi-sweet chocolate chips until evenly distributed.
Microwave on high for about 1 minute, checking at 45 seconds and adding 15-second bursts as needed, until the brownie is set but still fudgy in the center.
Allow to cool slightly, then optionally top with ice cream or whipped cream and serve immediately.
Notes
Best enjoyed fresh and warm. Adjust cooking time based on your microwave's power.