Thick, chewy, fudgy, and irresistible, these toffee butterscotch brownie cookies will be a new family favorite, and they're easy to mix by hand in one bowl!
Preheat the oven to 350 degrees F (180 C). Line baking sheets with parchment paper or silicone mats and set aside.
In a large microwave-safe bowl, combine the butter and chopped chocolate. Microwave on 50% power in 30-45 seconds bursts, stirring in between each, just until the mixture is melted and smooth. (You could also do this in a bowl set over boiling water on the stovetop.)
Add the sugar, salt, and vanilla extract; stir to combine. Add the eggs and stir again until fully incorporated.
Sprinkle the flour and baking powder on top of the batter, and stir gently just until incorporated. Finally, fold in the toffee and butterscotch chips.
Scoop the batter into 12 balls and arrange on the baking sheets, spaced about 2 inches (5 cm) apart. Bake for about 8 minutes, until the cookies puff up and crack slightly, and are just barely set. (They are meant to be soft, and will continue to set and firm up after coming out of the oven.)
Immediately after removing cookies, sprinkle with a few additional butterscotch chips, if desired, and a dusting of fine sea salt. Let cool on the baking sheets for about 10 minutes, then transfer to a wire rack to cool completely.
Notes
Cookies will keep well in an airtight container at room temperature for about 3 days.
The base recipe here is adapted from a fudgy walnut cookie found in One Bowl Baking by Yvonne Ruperti, which is probably my favorite cookbook acquisition in the past year. I highly recommend it!