Two Cups Flour

Homemade Toffee Bits
0 Line a baking sheet with a silicone baking mat or parchment paper and set aside. DO NOT use wax paper, the high heat from the toffee can melt it!
15 Place a small heavy-bottom saucepan on medium heat. Add in the butter, brown sugar, and salt. Stir as the butter melts. 
16 Once the butter is melted, whisk vigorously to combine. (vigorously is important at first! stir to slow and it will separate) Continue whisking constantly as the mixture cooks, to prevent burning. It should go from a dark brown color to a lighter caramel color.
1 If the mixture does separates while it's cooking, remove saucepan from the heat and stir vigorously again until it comes back together. Return pan to the heat and continue cooking.
2 Cook until it begins to resemble peanut butter 7-9 minutes, an instant read thermometer should read to 295°F (146°C) for "hard crack" candy.
3 Immediately remove from heat and pour the toffee onto the prepared baking pan. It should be easy to pour but have a thick texture. Careful when pouring as the mixture will be very hot. Spread the toffee into an even layer with a silicone spatula. The toffee will start to firm as soon as it hits the tray.
5 Let cook for about 20 minutes, or until it reaches room temperature. It should be firm enough to pick up into one big sheet of toffee. 
18 Chop the toffee into small chunks with a large knife, just like you would chocolate chips and set aside. 
24 Measure out 100 grams (1 cup) of the chopped toffee bits for the cookie dough. Store the leftovers in a plastic bag in the fridge for another recipe. 
Toffee Cookie 
17 In a medium bowl, whisk together the flour, baking soda, baking powder, cornstarch, and salt. Set aside. 
6 Place butter, brown sugar, and granulated sugar in the bowl of a stand mixer or large bowl with electric hand mixer.  Cream together on medium-high speed for about 2-3 minutes until whipped and light brown. All sugar granules should be well incorporated.
19 On medium speed, beat in the egg and egg yolk until well combined. Followed by the vanilla. 
8 Mix in the flour mixture, half at a time until just combined. 
10 Add the toffee bits and mix on low for a couple spins, just to mix them in. Or use a sturdy silicone spatula to fold them in by hand and avoid overworking the cookies dough.
20 Pre-scoop the cookie dough using a large cookie scoop. Place the portions on a parchment paper lined tray or air tight container. Cover and refrigerate for a minimum of 3 hours or overnight. 
11 Preheat oven to 350℉ (180℃). Line a cookie sheet with parchment paper.
21 Place cookie dough balls about 3-inches apart of the baking sheet. I bake four large cookies at a time. 
12 Place tray on middle oven rack and bake for 14-16 minutes. The centers should look puffy and the edges a golden brown. 
22 Transfer cookie sheet to a wire cooling rack and sprinkle with flaky sea salt. If the cookies are slightly misshapen, use a large round cookie cutter or glass to "scoot" around the cookie in a circular motion to re-shape them into a circle. (*see post for details) 
23 Leave cookies on the hot pan for about 10 minutes to finish setting up. Then transfer directly onto a wire rack to cool completely.