Preheat oven to 350°F.
In a medium mixing bowl, add the egg, buttermilk, oil and vanilla extract, beat to combine.
In a small mixing bowl, sift together flour, sugar, Matcha green tea powder, salt, baking powder and baking soda, or just mix with a wired whisk.
Slowly add the flour mixture to the liquid with the mixer on low speed.
Spray, oil or butter the donut pan cavities.
Spoon about 1/4 cup of batter into each cavity; try to distribute the batter evenly in the ring shape cavity.
Bake for 12 minutes until a toothpick inserted in the middle of donuts comes out clean.
Remove from the oven and flip the pan over on top of a wire rack to remove the donuts from the pan and let them cool on the wire rack.
For the ganache, add the chocolate and butter to a heat proof bowl.
Bring the heavy cream to a simmer in a small sauce pan over medium heat, remove from heat and pour it over the chocolate. Allow the mixture to stand a few minutes until the chocolate softens.
Whisk the hot cream and chocolate mixture gently until smooth and shiny.
Dip one side (or both sides) of the donuts into the ganache, twist it around gently to get as much ganache on the donuts as you’d like.
Store in an air tight container, they will last for a few days.