Combine flour, sugar, baking powder and matcha powder in a small bowl. Make sure to thoroughly mix before adding in liquids or else the matcha powder will separate and you'll end up with many chunks of matcha powder that won't smooth out.
Add in the egg and milk and stir until smooth. There may be a few bits of matcha powder that don't completely mix, but that's okay. You'll just have a few dark green specks in your mochi.
Take 2 teacups, pour half of mixture into one and half into the second tea cup. Cook 1 teacup in microwave for 1 min 30 seconds. Repeat with second tea cup.