In a microwave-safe bowl, whisk together glutinous rice flour, granulated sugar, and milk until smooth. Cover the bowl and heat in the microwave for two minutes, stirring after each minute until thick and slightly translucent.

Remove from the microwave and stir in melted coconut oil until fully combined. Allow to cool for at least 10 minutes.

Dust a clean surface with cornstarch. Turn the mochi mixture onto the surface and knead gently until smooth. Divide into 12 equal portions, rolling each into a ball and coating lightly with cornstarch.

Finely grind the loose-leaf Thai tea. In a mixing bowl, combine the ground tea with milk, all-purpose flour, baking powder, kosher salt, softened butter, eggs, and vanilla extract. Mix until just combined.

Cover the dough with plastic wrap and refrigerate for 2 hours or overnight.

Preheat your oven to 350°F (180°C). Line a baking sheet with parchment paper. Portion the chilled dough into balls, flatten each slightly, and place a mochi portion in the center, wrapping the dough around it.

Roll each cookie in granulated sugar followed by powdered sugar. Arrange on the baking sheet, leaving space between them, and bake for 12-15 minutes.

Cool on wire racks before serving.