Combine all crumble ingredients in a bowl and mix by hand until crumbly. Store in the freezer until ready to use.

In a bowl, beat softened butter with a hand mixer until smooth.

Add sugar and beat until light and fluffy.

Gradually add beaten eggs in 2-3 batches, mixing well each time.

Sift dry ingredients into the mixture and fold with a spatula.

Add heavy cream and mix until combined.

Transfer the batter to a piping bag and pipe into muffin tins lined with parchment paper.

Add a dollop of sweet red bean paste to the center of each muffin.

Sprinkle matcha crumble over the muffins.

Bake in a preheated oven at 175°C for 25-30 minutes.