Place the unsalted butter and eggs at room temperature overnight (this step applies in the winter).
Preheat the oven to 356°F (180°C). Lightly grease a 19.5 x 9.4 x 5.2 cm loaf pan with butter. Dust with flour, shaking off any excess. You can also line the pan with parchment paper.
In a medium bowl, add unsalted butter and sugar. Whisk until the butter becomes light and white-ish in color. This takes approx 4-5 minutes.
Add one egg at a time into the mixture. Whisk until it fully incorporates before adding more eggs. It is important that the eggs are at room temperature, otherwise, the mixture may curdle.
All-purpose flour + jasmine tea powder should equal 110g. Therefore, I recommend weighing the 1½ tbsp jasmine tea powder first, before adding the all-purpose flour.
Sift the all-purpose flour, jasmine tea powder, and baking powder into the mixture. Use a spatula and mix (using the cut-and-fold method) until just combined.
Transfer the batter to the loaf pan and smooth it out with a spatula.
Bake for 30 minutes or until the skin on top starts to form. Bring out the cake from the oven. At this time, the center of the cake should be slightly runny. Use a knife and carefully make a 1 inch deep cut in the middle of the cake.
Before the cake turns cold, put it back into the oven. Continue to bake for 15-17 minutes until the surface turns golden brown.
Leave the cake in the pan for 5-10 minutes, before transferring it to a cooling rack. Ready to serve.
The loaf pan that I used is 19.5 x 9.4 x 5.2 cm. You can also substitute with mini loaf pans instead.