Preheat the oven to 375°F (190°C). Line 17x11in (43x28cm) deep baking sheet with a parchment paper and spray cooking spray all over the parchment paper and on the sides.

In a large jug, combine the eggs, buttermilk and vanilla extract. Beat lightly and set aside. You should get about 1 ¼ cup of mixture.

In a large mixing bowl with a paddle attachment, or using a handheld electric mixer, mix together flour, sugar, baking powder, baking soda and salt. Add butter cubes just a few at a time while the mixer is running on slow speed. The flour mixture should get coarse texture with some pea size butter in there.

Pour about 2/3 of the egg mixture into the flour and beat until just combined. Then slowly pour the remaining egg mixture while the mixer is running. Beat till just combined. The batter might curdle slightly, and that’s normal. Pour the batter into the prepared baking sheet and tap a few times to get rid of bubbles. Bake for 15-18 minutes, or until the top is golden brown and inserted toothpick comes out clean.

Transfer onto a cooling rack to cool for 5 minutes. Then invert onto a wire rack, peel off the parchment paper and then invert it again so that the top of the cake is up. Cool completely.

While the cake is cooling, prepare salted caramel tea syrup. Dissolve the sugar in the boiling water and steep the tea for about 5 minutes. Let it cool.

To make the caramel buttercream frosting, beat the butter in large mixing bowl with paddle attachment, or using a handheld electric mixer, until fluffy, about 2 minutes. Add the powdered sugar and beat until well combined. Stir in dulce de leche and continue to beat until smooth, 1-2 minutes. Transfer the frosting into a piping bag with a round tip.

Once the cake is cooled completely, cut out 2-inch circles using a round cookie, or biscuit cutter. You will get about 35 circles. Place the cut out cake circles on wire rack and brush on the salted caramel tea syrup 3-4 times. Don’t overdo it, or the cakes will be too soggy. Pipe about heaping tablespoon of frosting on half of the cake circles. Using an offset spatula lightly spread the frosting and top with remaining plain cake circles. Frost the second layer the same way. Dust some sprinkles if desired.