Browning the butter helps create the base of the toffee flavour that is enhanced by the toffee bits. Dark chocolate and flaked salt simply adds to their decadence.
Cut butter into 1-inch (2.5 cm) chunks and place in a light-coloured small skillet (This will help you see the milk solids change colour). Place over medium heat and melt butter, stirring occasionally. Once butter is melted, cook the butter, stirring milk solids off bottom and sides of the skillet, constantly for 3 to 4 minutes until milk solids become golden and have a toasty aroma. Transfer butter to a large bowl and refrigerate for about 30 minutes to chill.
Meanwhile, in a bowl, whisk together flour, baking soda, baking powder and salt.
Remove bowl with butter from refrigerator. Whisk in brown and granulated sugars until looks creamy. Whisk in eggs, one a time and whisk in vanilla. Using a wooden spoon, stir in flour mixture until most of the flour is absorbed. Stir chocolate and toffee bits into flour mixture until evenly distributed and no flour remains.
Preheat oven to 350ºF (180ºC). Line a baking sheet with parchment paper; set aside.
Using a 1/4 cup (60 mL) dry measure, scoop out dough and place on prepared sheet. Repeat with dough leaving about 2 inches (5 cm) between each cookie. Sprinkle cookie dough lightly with salt. Bake for 10 to 12 minutes or until light golden around edge and top is just set but still soft.
Let cool on baking sheet on a cooling rack for 10 minutes before transferring cookies to cooling rack to cool completely. Repeat with remaining cookie dough (be sure baking sheet is cool before adding dough).
You can portion out the dough and refrigerate for up to 3 days or freeze for up to 3 months.
Baked cookies can be frozen for up to 2 months.
Bake 1 sheet at a time in the centre of the oven. You can prepare a second tray if you have one to speed up the baking time.