Preheat the oven to 400°F (200°C). Line a 9×9 pan with parchment paper and arrange the saltine crackers in a single layer.

In a small saucepan, combine 6 tbsp salted butter and 6 tbsp brown sugar. Bring to a boil over medium heat and let it boil for 2 1/2 minutes without stirring.

Pour the hot toffee over the saltine crackers, spreading gently if needed.

Bake the toffee-covered crackers for 6 minutes.

Remove from the oven and immediately sprinkle 3/4 cup chocolate chips on top. Let them sit for 5 minutes, then spread the melted chocolate evenly.

Let the cracker toffee cool completely, then put it in the freezer to firm up.

While the toffee chills, brown the butter for the cookie dough: in a medium saucepan over low heat, melt 1 cup salted butter and heat until it bubbles, turns golden brown, and smells nutty. Remove from heat and let cool slightly.

Pour the brown butter into a large mixing bowl or the bowl of a stand mixer.

Add 1 cup brown sugar and 1/2 cup granulated sugar to the brown butter. Mix well for 1 minute.

Add 2 eggs and 1 tsp vanilla, mixing until smooth and no longer grainy.

Add 2 1/4 cups flour, 1 tsp baking soda, and 1/2 tsp salt. Mix until combined; dough should be very soft.

Remove the cracker toffee from the freezer and chop it into small pieces.

Fold the chopped cracker toffee into the cookie dough.

Scoop the dough into 3 tbsp portions and place on parchment or silicone-lined baking sheets. Sprinkle each with flaky sea salt.

Let the cookie dough rest at room temperature for 10 minutes before baking.

Preheat the oven to 350°F (180°C).

Bake cookies for 9–11 minutes, or until they have spread and no longer look glossy. Let the cookies cool on the pan.