Preheat oven to 175C. Prepare liners/cups.
Heat milk and condensed milk over medium or medium-high heat until scalded – steaming with bubbles forming around the edge – stirring occasionally (Make sure not to burn the mix!). Add the tea mix, remove from heat, cover, and let sit 10 minutes.
Pour through a sieve, coffee filter, or tea screen to strain out the tea. Let the mixture cool to somewhere between room temperature, using the refrigerator or freezer to cool down quickly if necessary.
Whisk together the flour, baking powder, and salt in a large bowl. Set aside.
Using an electric mixer (stand or handheld) on medium speed, cream together the butter and sugar until light and fluffy (4-6 minutes). Beat in the eggs one at a time, making sure each egg is fully incorporated before adding the next. Beat in the vanilla. Scrape down the beaters and the sides of the bowl as needed.
Folded in the flour and milk (alternate, starting with flour), by hand.
Pour the batter into the prepared pan(s), filling cupcake cups about 2/3 full. Bake 20-30 minutes.
Let the cakes cool on wire rack.