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Make brown butter: Melt the butter in a heavy-bottom pan over medium heat. Frequently stir until it turns golden brown with a few specks of brown bits visible.
Then transfer immediately into a measuring jar to stop it from cooking further in the hot pan. Weigh the amount as you transfer because we need to divide it evenly into three equal portions. Also, stir the brown bits in the butter before each pours to distribute them evenly. Each portion will be used for each cookie dough.
Make cookie dough (same method for the 3 kinds of cookie dough): Into a portion of the brown butter, add sugar, and mix well with a silicone spatula.
Let the butter comes to room temperature. Then sieve in flour and baking powder. Add salt and the flavoring ingredient (almond extract/ matcha powder/ cocoa powder). Mix well.
Form it into a ball. If the mixture is crumbly (this can happen when the brown butter has turned solid), simply knead it with your hand. The warmth from our hand will bring the mixture together. Wrap with plastic and refrigerate for 30 minutes.
Place the dough in between 2 sheets of parchment paper. Using a rolling pin, press it down a couple of times to flatten it out before rolling. Roll to 1/4" (0.6 cm) thickness.
Remove the top sheet of paper. Cut out as many circles with a cookie cutter. Transfer them onto a tray lined with parchment paper. Bring together the leftover dough and repeat the rolling process. If using a 2" (4.8 cm) in diameter cutter, you should be able to get 12 circles for each cookie dough.
Bake in a preheated oven at 375F (190C) for 15 minutes or until lightly browned.
Filling and assembly: Melt the chocolate over a double-boiler. White chocolate can easily turn lumpy when overheated, so heat just until it melts.
Turn half of the cookies up-side-down. Either with a spoon or piping bag, add enough chocolate filling onto the center of these cookies. Top each with another cookie to make a sandwich. Then enjoy!
