Preheat the oven to 350 degrees Fahrenheit. Line a baking sheet with parchment paper, and set it aside.
Make the brown butter by heating 8 tablespoons butter in a saucepan over medium heat until brown bits form. Try not to walk away as it can burn very quickly. Immediately remove the butter from the heat, and set it aside to cool completely.
8 Tablespoons unsalted butter
In a large mixing bowl, whisk together the flour, baking soda, and salt.
2 cups all-purpose flour, 3/4 teaspoon baking soda, 1/2 teaspoon salt
In a separate large bowl, whisk together the brown sugar, white sugar, softened butter, and cooled brown butter until smooth. Add the whole egg, beat for 1 minute. Scrape down the sides and the egg yolk and vanilla. Beat until fluffy 1-2 minutes.
9 Tablespoons unsalted butter, 3/4 cup granulated sugar, 3/4 cup packed brown sugar, 1 large egg, 1 egg yolk, 1/2 teaspoons vanilla
Add the dry ingredients to the bowl with the we ingredients. Stir until no streaks of flour remain. Be careful not to overmix!
Gently fold in the toffee bits.
6 ounces toffee bits
Use a large cookie scoop to portion out the dough into equal-sized portions. Arrange them on a baking sheet.
Bake for 9-10 minutes or until the edges are golden brown.
Transfer to a cooling rack.