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.
Add the egg and egg yolk and vanilla extract to the butter and sugar mixture. Mix until well combined.
In a separate bowl, whisk together the all-purpose flour, baking soda, and 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.
Using a cookie scoop or a spoon, drop ¼ 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.
