Gather all the ingredients listed above. Make sure you have everything measured out to make the mixing process easier.
In a mixing bowl, whisk together the gluten-free all-purpose flour, matcha powder, baking powder, and a pinch of sea salt until well combined.
Add the egg yolk, pure maple syrup, and coconut milk to the dry mixture. Use a whisk or fork to mix everything until you have a smooth batter.
Gently fold in the white chocolate chips into the batter, ensuring they are evenly distributed.
Pour the batter into your microwave-safe mug, filling it about halfway to allow room for rising.
Place the mug in the microwave and cook on high for about 1 minute and 30 seconds. Cooking times may vary, so keep an eye on it to avoid overflowing.
Once cooked, allow your Matcha Mug Cake to cool for a minute or two before enjoying. It will be hot!