Preheat the oven to 350 degrees F. Line 2 baking sheets with parchment paper. Whisk the flour and baking soda in a bowl.

In a stand mixer fitted with the paddle attachment, cream the butter, brown sugar and granulated sugar on low speed until incorporated, then increase to high speed and beat until light and fluffy.

Add the salt, vanilla, whole egg and egg yolk to the mixer; beat until thoroughly combined. Add the Pretzel M&M'S and beat for a few seconds until slightly crushed. Gradually add the flour mixture, mixing on low speed until just combined. Mix in the bittersweet chocolate, toffee pieces and peanut butter chips.

Roll heaping tablespoonfuls of dough into balls and place on the prepared baking sheets, about 2 inches apart. Slightly flatten each ball with your fingers.

Bake the cookies until the edges are golden brown and the centers are no longer wet, 11 to 13 minutes. Cool on the baking sheets for a few minutes, then transfer to a rack to cool completely.

Photograph by Charles Masters