Weigh butter, cut into small pieces and place into small saucepan, cook under low heat until butter molten and bubbles into brown color, turn off heat; Pour browned butter into large bowl, place in refrigerator to cool until butter solidifies but not too hard; Add castor sugar and powdered sugar in the butter above, mix until blended, beat mixture with whisk briefly; Add eggs into whisked butter; Mix with spatula until no fine particles are left; Chop pistachio kernels and add into cake batter; Mix pistachios and batter with hand and roll batter into a ball; Place batter on kneading board and roll dough into elongated shape, then place into freezer for 1/2 to 1 hour until completely hardens;  Remove dough from freezer and cut into 0.3cm thick slices; Place slices on baking pan, left sufficient space between biscuits, place in oven pre-heated to 180℃ for about 15 minutes until the biscuits turned golden brown in color.