Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper and set it aside.

Place the 2 sticks (1 cup) salted butter in a skillet over medium heat. Cook, stirring occasionally, until the butter foams, the milk solids turn golden-brown and the butter smells nutty, about 3–4 minutes. Remove the skillet from the heat.

Pour the browned butter into a heatproof bowl and let it cool until warm but not hot, about 5 minutes (cooling prevents the eggs from cooking when added).

Add the 2/3 cup brown sugar, 1/3 cup granulated sugar, 2 large eggs, and 1 tablespoon vanilla extract to the warm brown butter. Stir or whisk until the mixture is smooth and uniform.

Add 2 1/4 cups all-purpose flour, 1 teaspoon baking soda, and 1/2 teaspoon kosher salt to the butter mixture. Stir until just combined and no large dry streaks remain—do not overmix.

Gently fold in the 1 1/2 cups chopped chocolate chunks or chips and 3/4 cup raspberries (fresh or frozen), taking care not to break up the raspberries.

Use rounded tablespoon-size portions of dough to form balls and place them about 2 inches apart on the prepared baking sheet. If the dough is wet from the berries, gently flatten each mound with the back of a spoon or your fingers.

Bake on the middle rack for 8 minutes. Remove the baking sheet, rotate it, and tap it firmly on the counter 1–2 times to help the cookies flatten.

Return the baking sheet to the oven and bake 2–3 more minutes, until the cookie edges are just beginning to set and the centers still look slightly soft.

Let the cookies cool on the baking sheet; they will continue to set as they rest. Sprinkle with flaky sea salt if desired. Store cooled cookies in an airtight container for up to 4 days.