In a saucepan, melt the butter over medium heat. Stir continuously until it foams and the milk solids turn golden and nutty. Pour into a bowl and let cool for at least 10–15 minutes.

After the brown butter has cooled whisk in both sugars until combined. Add the egg, egg yolk, and vanilla. Mix until glossy.

In a separate medium bowl whisk flour, baking soda, and salt.

Pour flour into the bowl with the wet ingredients, until just combined.

Add chocolate, toffee bits, and pretzel pieces. Gently fold until evenly distributed.

With a large cookie scooper scoop 12 dough balls onto parchment-lined baking sheet or a large bowl.

Cover and refrigerate for at least 1 hour, or overnight for best flavor.

Preheat oven to 175°C / 350°F.

Place the dough balls onto parchment-lined baking sheets. Leave room for spreading.

Bake for 11–13 minutes, or until edges are golden and centers are just set.

Sprinkle with flaky salt right out of the oven if you like.

Let cool on the tray 5 min before transferring to a rack.