Preheat the oven to 160°C/320°F (convection). Whisk butter and sugar in a large bowl until creamy. Gradually stir in the eggs and beat the mixture until foamy.
Combine flour, baking powder, matcha powder, and salt in a medium bowl. Add milk and, if desired, vanilla extract.
Add the matcha mixture into the butter mixture and mix well. Fill into the muffin liners and muffin tin. Bake the cupcakes at 160°C/320°F (convection) for approx. 20 min. Let them cool for approx. 8 – 10 min. Decorate as desired.