• Preheat the oven to 350 F (180 C) for conventional oven. For a convection oven, please lower the temperature by 20 F (15 C)
• Lightly grease the the pan with some oil and line with two sheets of parchment paper, perpendicular and overhanging on the side. You can use 8 x 8 inch square pan or 9-inch round pan

Prepare the crumbs:

• Combine all ingredients in a bowl. Rub the dry ingredients with the butter to form some small and large clumps. Keep them chilled in the fridge while you prepare the rest
  

Prepare the filling:

• Simply combine matcha powder with sugar and set aside
  

Prepare the cake batter:

• Combine flour, sugar, baking powder, salt, and baking soda in a mixing bowl of a stand mixer fitted with paddle attachment. Add softened butter. Start the machine on low to mix them into sandy texture
  
• Add room-temperature eggs and vanilla and mix on medium speed into a thick paste.
  
• Add sour cream/Greek yogurt and continue to beat until the mixture is smooth, thick, and creamy, about 4-5 minutes on high speed
  

Assembling:

• Spread half of the cake batter into the base of the pan. Use an offset spatula to help you spread it evenly
  
• Sprinkle with the filling all over the surface of the batter.
  
• Dollop the rest of the batter for easier spreading
  
• Uuse an offset spatula to spread again. Smooth the batter
  
• Remove the crumbles from the fridge. Break some large clumps (if they are too large). Sprinkle evenly on top of the batter and just lightly press the crumbles on the batter so they stick better after baking
  

Bake:

• Place the pan in the middle rack and bake for 45-50 minutes or until a cake tester inserted into the center of the cake comes out with just a bit of moist crumbs, but it shouldn't be wet

Cool down:

• Set the pan on top of a cooling rack and let it cool down inside the pan for 20 minutes. Then grab the overhanging parchment paper and lift the cake out of the pan and let it cool down completely on the rack