Brown the butter: Place 113g unsalted butter in a light-colored saucepan over medium heat. Cook until it melts, foams, and golden brown specks appear. Immediately pour into a large heat-safe bowl. Cool for 10-15 minutes.
Whisk dry ingredients: In a medium bowl, whisk together 250g (2 cups) flour, 1 teaspoon baking soda, and ¾ teaspoon salt. Set aside.
Cream butter and sugars: To cooled browned butter, add 100g (½ cup) brown sugar and 60g (⅓ cup) granulated sugar. Beat on medium speed for 2-3 minutes until combined and slightly fluffy.
Add wet ingredients: Add room temperature egg and 1½ teaspoons vanilla extract. Beat until smooth and glossy, scraping bowl as needed.
Combine: With mixer on low, gradually add dry ingredients. Mix just until no flour streaks remain. Do not overmix.
Crush pretzels: Place pretzels in a zip-top bag and crush with a rolling pin until you have a mix of fine crumbs and chunks.
Add mix-ins: Using a rubber spatula, fold in 200g (1¼ cups) chopped chocolate and crushed pretzels until evenly distributed.
Chill: Cover dough and refrigerate for at least 1 hour (up to 3 days).
Preheat and prep: Preheat oven to 375°F (190°C). Line baking sheets with parchment paper.
Scoop: Scoop dough into 3-tablespoon balls (about 65g each). Place on prepared sheets, 3 inches apart.
Top: Gently press extra pretzel pieces into each dough ball. Sprinkle with a tiny pinch of flaky sea salt.
Freeze (optional but recommended): Freeze dough balls for 24 hours for best texture and flavor.
Bake: Bake for 11-13 minutes until edges are golden and centers still look soft.
Cool: Let cookies cool on baking sheet for 10 minutes. Transfer to wire rack.
Serve: Enjoy warm or at room temperature.
