Preheat oven to 350 degrees F (177 degrees C).
Prep donut pan by greasing it with oil or butter. I used a donut pan with donut molds that are 3 inches in diameter. Set aside.
Add 3 tbsp of unsalted butter to a large bowl. Microwave for 30-40 seconds until completely melted. You might need to adjust the time period depending on how strong your microwave is.
Once melted, add ½ cup of light brown sugar, ½ cup of coconut milk, 1 egg, ½ tsp of vanilla extract, and ¼ tsp of salt to the bowl. Mix until combined.
Combine the last 2 tbsp of unsalted butter and 4 oz of chopped dark chocolate in a separate bowl. Microwave for 30-40 seconds until the chocolate fully melts. You might need to adjust the time period depending on how strong your microwave is. Mix until smooth.
Add the melted chocolate to the batter and mix until combined.
Lastly, add 1 tbsp of cocoa powder, ⅔ cup of sweet flour, and 1 tsp of baking powder to the batter. Mix until a thick batter forms.
Spoon the dough into a pastry bag or Ziploc bag. Pipe the donuts into the prepared donut pans.
Bake for 12-14 minutes until a toothpick comes out clean.
Let donuts cool in the donut pan for 10 minutes. Transfer to a cooling rack to cool completely.
Once cool, dip the donuts in the matcha ganache and enjoy! Alternatively, you can opt to spoon the ganache over the donuts. Make sure to place some parchment paper under the cooling rack for easy clean up.