Prepare Browned Butter: In a medium saucepan over medium heat, melt unsalted butter. Stir continuously until it becomes foamy and turns golden brown (about 5 minutes). Once browned, chill in the refrigerator until solid (approximately 45-60 minutes).

Preheat Oven: Preheat your oven to 350°F (175°C).

Mix Dry Ingredients: In a large mixing bowl, sift together all-purpose flour, baking powder, kosher salt, and baking soda. Set aside.

Cream Butter and Sugars: Beat the browned butter with dark brown sugar and granulated sugar for about 3 minutes until light and fluffy. Add in the egg and vanilla extract.

Combine Mixtures: Gradually add the dry mixture to the wet mixture, mixing until just combined. Fold in the chopped white chocolate, salted pistachios, and dark chocolate.

Form Dough Balls: Scoop the dough into 1-inch balls and place in a non-stick mini muffin tray, spacing them about 2 inches apart.

Bake: Bake for 12-14 minutes until edges are set but centers remain soft. Press down in the center of each cup to create wells.

Cool and Fill: Cool in the tray for 15 minutes, then transfer to a wire rack. Fill each cup with pistachio cream and drizzle melted chocolate on top.

Refrigerate: Place filled cookie cups in the refrigerator for about 5 minutes to set the chocolate.