Preheat oven to 350°F (177°C). Line two baking sheets with parchment paper.

In a medium bowl, whisk together the flour, salt, and baking powder until well combined. Set aside.

In the bowl of a stand mixer, with the paddle attachment, cream the butter with the Redpath® Granulated Sugar on medium speed until fluffy and pale in colour; about 3 minutes. Add the egg and vanilla extract. Blend until the egg and vanilla extract are fully incorporated into the batter.

On low speed, add about half of the dry mixture to the bowl, until barely combined. Add the remaining flour. Mix until it just forms a dough; do not overmix.

Divide dough in half. On one half of the dough, sprinkle the matcha green tea powder.

Gently knead until combined. On the other half, sprinkle the ground black sesame seeds, and the whole black sesame seeds.

Wrap each coloured dough in plastic wrap and chill in the fridge for at least 30 minutes.

When ready to use, allow dough to come to room temperature; about 5 minutes.

Place the matcha dough between 2 sheets of parchment. Roll dough to a ¼-inch (6 millimetre) thickness. Using a 2-inch round cookie cutter, cut out rounds. Scraps can be gathered and rerolled and cut. Repeat process with the black sesame cookie dough.

Transfer cookies onto prepared baking sheet. Place cookies into the fridge or freezer to chill before baking; about 10 minutes. Place cookies into the preheated oven for 10 to 12 minutes. Take out of the oven.

Cool for 5 minutes on the baking sheet. Transfer to a wire rack to cool completely.

In the bowl of a stand mixer, with the paddle attachment, cream butter until smooth; about 2 minutes. Sift in the Redpath® Icing Sugar and salt. Blend until sugar is incorporated into the butter. Add in the ube flavouring, beat mixture on medium-high speed until fluffy. 

Transfer frosting into a piping bag fitted with a small plain piping tip.

Pipe about a tablespoon of the icing onto half of the bottoms of each type of cookie. Top with either the opposite or same cookie. 

Store cookies in an airtight container at room temperature for up to a week, or in the freezer for up to 2 months, between layers of parchment paper.