In a medium, microwave-safe mug (about 10-12 oz), whisk together all the dry ingredients: flour, sugar, matcha powder, baking powder, and salt until thoroughly combined and there are no visible clumps of matcha.

Add the wet ingredients directly into the mug: milk, vegetable oil, and vanilla extract.

Using a small fork or mini whisk, gently mix the wet and dry ingredients until just combined. Be careful not to overmix; stop stirring as soon as no dry streaks remain. The batter should be smooth.

Wipe down the edges of the mug if necessary. Place the mug in the center of the microwave.

Microwave on High for 60 to 90 seconds. Cooking time may vary based on microwave wattage. Start checking at 60 seconds; the cake is done when it looks set on top but is still slightly soft.

Let the mug cake cool for 1-2 minutes before eating directly from the mug or carefully inverting onto a small plate. Garnish optionally with powdered sugar or whipped cream.