Preheat oven to 400 degrees F.
Prep your ramekins. Brush 2 ramekins with melted butter. Use ramekins that are 4 inches in diameter. Next coat the ramekin with sugar. Make sure the entire inside is coated. Set ramekins aside.
Matcha Base: Add the matcha powder and milk to a small sauce pan and whisk. Heat for a few seconds over low heat until smoke is emitted from the mixture. Remove pan from the heat. Whisk together sugar and egg yolks in a separate bowl. Add the sugar/egg yolk mixture to the sauce pan. Mix all the ingredients together. Finally, add in the flour and mix well. Return the sauce pan to the stove and heat the mixture over low heat until it is a thick consistency. The mixture should be the consistency of honey. Remove the saucepan from the heat and set aside to cool.
Meringue: Add cream of tartar to the egg whites. Using a hand mixer or stand mixer, whip your egg whites on low speed. Once you see soft peaks form, slowly add in the sugar. Turn up the speed of your mixer to high. Whip your meringue until you see stiff peaks. Be careful not to over whip your meringue.
Empty the matcha base into a medium-sized bowl. Add 1/4 of your meringue to the matcha base and mix.
Add the rest of your meringue. Gently fold the meringue into your matcha base. Use big circular motions around the edge of the meringue to incorporate in the matcha base. Be careful not to deflate your meringue.
Spoon the souffle into your prepared ramekins. Over fill your ramekins and level them off with a straight edge. Once filled, trace the inside edge of your ramekin with your thumb to create an indentation.
Bake souffle for 11-13 minutes or until the souffle has risen above the ramekin and the edges are slightly golden brown.
While the souffle is baking, make the matcha sugar by combining matcha powder and powdered sugar. Set aside.
Once out of the oven, sprinkle the souffle with matcha sugar and serve immediately. Souffles start to deflate once they come out of the oven, so they are best served right away.