Whisk the flour, cocoa powder, baking powder and salt together until combined. Set aside.

In a large bowl using a handheld or stand mixer fitted with a paddle attachment, beat the butter for 1 minute on medium speed until completely smooth and creamy. Add the granulated sugar and brown sugar and beat on medium high speed until fluffy and light in color. Beat in the vanilla on high speed. Scrape down the sides and bottom of the bowl as needed.

On low speed, slowly mix the dry ingredients into the wet ingredients until combined. The cookie dough will be thick. Switch to high speed and beat in the milk, then the butterscotch and toffee. The cookie dough will be sticky. Cover dough tightly with aluminum foil or plastic wrap and chill for at least 3 hours and up to 3 days. Chilling is mandatory for this cookie dough. I always chill mine overnight.

Remove cookie dough from the refrigerator and allow to sit at room temperature for 20 minutes—if the cookie dough chilled longer than 3 hours, let it sit at room temperature for about 30 minutes. This makes the cookie dough easier to scoop and roll.

Preheat oven to 350°F (177°C). Line two large baking sheets with parchment paper or silicone baking mats. Set aside.

Scoop and roll balls of dough, about 1.5 Tablespoons of dough each (I use this medium cookie scoop), into balls. Place on the baking sheets.

Bake the cookies for 12-13 minutes. My oven has hot spots and yours may too, so be sure to rotate the pan once during bake time. The baked cookies will look extremely soft in the centers when you remove them from the oven. Allow to cool for 5 minutes on the cookie sheet. During this time, you can press a few more butterscotch morsels into the top of the warm cookies—this is just for looks. You can also sprinkle with a little sea salt as well. The cookies will slightly deflate as you let them cool. Transfer to cooling rack to cool completely.