Step 1: Prep the Gooey Center: Scoop out about 1 tablespoon portions of the pistachio cream onto a parchment-lined sheet or plate and pop them into the freezer. Let them freeze while you make the dough.
Step 2: Brown That Butter: In a small saucepan, melt butter over medium heat, stirring occasionally. It will bubble, then foam. Continue stirring until brown bits form at the bottom, the butter is amber, and it smells nutty (5-8 minutes). Don't walk away!
Step 3: Chill the Butter: Immediately pour the warm brown butter into a medium mixing bowl, scraping in the brown bits. To speed cooling, pop the bowl into the freezer for about 5 minutes until it's no longer hot. Ensure you have at least 90g after browning (add water if needed).
Step 4: Whisk in Sugars: Once the brown butter has cooled (warm or room temperature), add the light brown sugar and granulated sugar. Whisk until well combined and it looks like a brown sugar paste.
Step 5: Add the Egg: Whisk in the room temperature egg until fully incorporated and the mixture looks smooth and glossy (30 seconds to a minute).
Step 6: Mix Dry Ingredients: Add the flour, baking powder, baking soda, and salt. Switch to a rubber spatula and gently fold until just a few streaks of flour remain. Stop here!
Step 7: Fold in the Goodies: Add the chocolate chips (or chunks!) and crushed pistachios. Gently fold until no dry flour streaks are visible. Be careful not to overmix.
Step 8: Stuff Those Cookies: Scoop out generous portions of dough (about 3 tablespoons each). Flatten a scoop in your palm, place a frozen pistachio cream ball in the center, and carefully gather the dough edges to completely enclose the cream. Pinch and roll gently to seal.
Step 9: Chill Out: Place stuffed cookie dough balls onto a plate or baking sheet. Cover loosely with plastic wrap and refrigerate for at least 30 minutes to help flavors meld and prevent excessive spreading.
Step 10: Get Ready to Bake: Preheat your oven to 350°F (175°C). Line a cookie sheet with parchment paper. Space out chilled cookie dough balls evenly on the sheet.
Step 11: Optional Pistachio Swirl: Gently melt a little extra pistachio cream (microwave in 15-second bursts). Spoon a tiny dollop or swirl onto the top of each cookie dough ball before baking.
Step 12: Bake 'Em Up: Bake for 12-14 minutes, watching around the 12-minute mark. Edges should be set and golden brown, centers slightly soft. They'll finish cooking on the hot pan.