Preheat oven to 325°F (170°C).

For cake: In a small microwave-safe bowl, heat milk and 1¼ teaspoons (3 grams) tea leaves on high in 20-second intervals just until steaming. Cover with plastic wrap; let cool completely.

In the bowl of a stand mixer, whisk together sugar, zests, and remaining 2½ teaspoons (6 grams) tea leaves by hand until sugar is fragrant. Add butter; using the paddle attachment, beat at medium speed until light and fluffy, 2 to 3 minutes, stopping to scrape sides of bowl. Add eggs, one at a time, beating well after each addition and stopping to scrape sides of bowl. Beat in vanilla.

In a medium bowl, whisk together flour, salt, and baking powder. With mixer on low speed, gradually add flour mixture to butter mixture alternately with cooled milk mixture, beginning and ending with flour mixture, beating until combined after each addition and stopping to scrape sides of bowl.

Spray a 10-cup Bundt pan with baking spray with flour. Spoon batter into prepared pan. Firmly tap pan on a kitchen towel-lined counter 7 to 10 times to level batter and release any air bubbles.

Bake until a wooden pick inserted near center comes out clean and an instant- read thermometer inserted near center registers at least 205°F (96°C), 1 hour to 1 hour and 5 minutes. Let cool in pan for 10 minutes. Invert cake onto a wire rack, and let cool completely.

For topping: In a small bowl, whisk together sugar and tea leaves. Using a pastry brush, brush melted butter onto cooled cake; sprinkle with sugar mixture, gently pressing to adhere. Best served same day as made. Store in an airtight container for up to 3 days.