Preheat the oven to 350 degrees Fahrenheit. Line baking sheets with parchment paper or silicone baking mats, and set aside.
In a large mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until the mixture is light and fluffy, which should take about 2-3 minutes.
1 cup 2 sticks butter, softened, 3/4 cup packed brown sugar, 3/4 cup granulated sugar
Add the egg and egg yolk and vanilla extract to the butter and sugar mixture. Mix until well combined.
1 large egg yolk, 2 teaspoons vanilla extract, 1 large egg
In a separate bowl, whisk together the all-purpose flour, baking soda, and salt.
2 1/4 cups all-purpose flour, 1 teaspoon baking soda, 3/4 teaspoon salt
Gradually add the dry ingredient mixture to the wet ingredients, mixing until the dough comes together.
Fold in the dark chocolate chips, semi-sweet chocolate chips, chopped pretzels, caramel, and toffee bits. If you're using flaky sea salt, you can sprinkle it on top of the cookie dough at this stage.
3/4 cup dark chocolate chips or chunks, 1/2 cup semi-sweet chocolate chips or chunks, 3/4 cup chopped pretzels, 3/4 cup caramel squares cut into small pieces, 1/2 teaspoon flaky sea salt, 1/2 cup toffee bits
Using a cookie scoop or a spoon, drop 1/4 cup of cookie dough onto the prepared baking sheets, leaving some space between each cookie. Note: refrigerate the dough for at least 1 hour or overnight.
Bake the cookies in the preheated oven for 10-12 minutes or until the edges are golden brown. The center should still be slightly soft.
Remove the cookies from the oven and let them cool on the baking sheets for a few minutes before transferring them to wire racks to cool completely.