Cream butter, brown sugar, and granulated sugar until light and fluffy.
Beat in egg and vanilla until smooth.
In a separate bowl, whisk flour, baking soda, baking powder, and salt.
Gradually mix dry ingredients into wet ingredients just until combined.
Gently fold in caramel bits, toffee bits, and pretzels or nuts.
Chill dough for 30–45 minutes.
Preheat oven to 350°F (175°C) and line baking sheets with parchment paper.
Scoop dough into balls (about 2 tablespoons each) and place 2–3 inches apart.
Bake for 10–12 minutes until edges are lightly golden and centers are soft.
Sprinkle flaky sea salt on warm cookies.
Cool briefly on the tray, then transfer to a wire rack.