Preheat the oven to 350°F and line baking sheets with parchment paper.
Whisk dry ingredients (2 min): In a medium bowl, whisk together the dry ingredients including the flour, baking soda, corn starch, and salt.
2 1/4 cups 270g all-purpose flour, 1 teaspoon baking soda, 1 Tablespoon 8g cornstarch, 1/2 teaspoon salt
Cream the butter & sugar (3 min): In a large bowl using a handheld or stand mixer fitted with a paddle attachment, beat the butter, brown sugar, and granulated sugar until light and creamy, 2-3 full minutes.
3/4 cup 170g unsalted butter,, 3/4 cup 150g light brown sugar,, 1/4 cup 50g granulated sugar
Add the wet ingredients (2 min): Add the egg, egg yolk, and vanilla, and beat for another 1-2 minutes, until light and fluffy, scraping down the sides of the bowl as needed.
1 egg, 1 egg yolk, 1 teaspoon vanilla extract
Add the dry ingredients (2 min): With the mixer on low, slowly add the dry ingredients and mix until combined.
Stir in the mix-ins (1 min): Add the chocolate chips, jimmies, toffee, potato chips, and pretzels and stir with a rubber spatula until combined.
1/2 cup semi-sweet chocolate chips, 3/4 cup crushed potato chips, 1/2 cup chopped pretzels, 1/4 cup holiday jimmies, 1/2 cup toffee bits
Bake (10 min): Use a large cookie scoop (or a scant 1/4 cup), to scoop out the dough and drop on the cookie sheets. Roll the dough balls into tall ovals (rather than balls) for thicker cookies. Bake for 10-12 minutes, until the edges are slightly golden and the tops are just set.
Finish the cookies: Immediately swirl the rim of a large glass gently around the outside of the warm cookies for perfect circle and press extra topping pieces on top. Transfer to a cooling rack after 5 minutes to cool completely.