Line a baking sheet with parchment paper and set aside.

In a small pot, melt 113 grams of butter. Add 200 grams of light brown sugar and 1 teaspoon of fine sea salt, whisking vigorously for one minute until combined.

Bring the mixture to a simmer while whisking often, letting the temperature rise to approximately 300°F.

If it separates, remove from heat and whisk until combined again.

Pour the hot mixture onto the prepared baking sheet, spreading it into an even layer. Let it cool and set.

Once hardened, break the toffee apart or coarsely chop it and set aside until ready to use.

Melt the remaining 184 grams of unsalted butter in a pot over medium heat. Allow it to crack and sizzle for a few minutes.

Stir until you see golden milk solids, and the butter becomes golden brown.

Transfer the butter to another container to stop cooking.

Once cooled (warm, not hot), add 100 grams of dark brown sugar, 100 grams of granulated sugar, and 1 tablespoon of vanilla extract, whisking to combine.

Next, add 1 egg and 1 egg yolk, whisking until mixed.

Whisk in 1 teaspoon of baking soda, 1 teaspoon of cream of tartar, 1.5 teaspoons of ground cinnamon, 0.5 teaspoon of fine sea salt, and 5 grams of cornstarch. Add 250 grams of all-purpose flour and fold until a few pockets remain.

Fold in the toffee until fully mixed. Cover tightly and chill the dough for at least 3 hours.

Preheat your oven to 350°F and line another baking sheet with parchment.

Scoop the dough and form cookies (about 1.125 oz each or around 40-50 grams).

Space the cookies on the baking sheet 2-3 inches apart. Bake for 8-10 minutes until the edges are set and centers are puffy.

Let them cool for 5-10 minutes on the baking sheet before transferring to a cooling rack.