Preheat oven to 350°F. Line two baking sheets with parchment.
Whisk flour, cornstarch, baking soda, and kosher salt in a bowl; set aside.
Cream softened butter, brown sugar, and granulated sugar until light and fluffy, about 2 minutes.
Beat in the egg, egg yolk, and vanilla until smooth and glossy.
Mix in the dry ingredients on low just until the dough comes together; do not overmix.
Fold in chocolate chips and chopped pistachios until evenly distributed.
Chill the dough 15–20 minutes to firm slightly for cleaner scoops.
Scoop 1½-tablespoon mounds onto sheets, spacing about 2 inches apart.
Bake 10–12 minutes, until edges are set and centers look slightly soft.
Cool on the sheet 5 minutes, sprinkle flaky salt if using, then move to a rack.
Notes
Try swapping half the semi-sweet chips for dark chocolate chunks or add 1 tsp orange zest for a bright twist. Store cookies airtight at room temperature up to 4 days, or freeze portioned dough balls for fresh-baked cookies anytime.This recipe is an original creation inspired by classic Easy Pistachio Chocolate Chip Cookies flavors. All ingredient ratios and instructions are independently developed.