# Steps:
01 - Place Oreo cookies in a microwave-safe mug and thoroughly crush with a fork until finely crumbled.
02 - Add milk to the crushed Oreos and mix until it forms a thick, soaked paste.
03 - Stir in all-purpose flour, granulated sugar if using, and baking powder until evenly combined.
04 - Mix in the small egg and vanilla extract if desired until the batter is smooth and uniform.
05 - Cook in the microwave on high power for 1 minute 30 seconds. Check that the cake is set but moist; if necessary, heat an additional 10 to 20 seconds.
06 - Allow the mug cake to cool for 1 to 2 minutes before enjoying directly from the mug.