M&M Pretzel Cookies are sweet, salty, and a little bit addicting! The browned butter gives these cookies a butterscotch undertone that makes them irresistible!
Adjust oven rack to middle position and heat oven to 375 degrees. Line 2 large (18- by 12-inch) baking sheets with parchment paper.
MAKE COOKIE BATTER:
Whisk flour and baking soda together in a medium bowl.
Heat 10 tablespoons of the butter in a 10-inch skillet over medium-high heat until melted, about 2 minutes. Continue cooking, swirling pan constantly until butter is dark golden brown and has a nutty aroma, 1 to 3 minutes.
Remove skillet from heat and, using a heatproof spatula, transfer browned butter to a large heatproof bowl using a heatproof spatula. Stir the remaining 4 tablespoons of butter into hot butter until completely melted.
Add both sugars, salt, and vanilla to bowl with butter and whisk until fully incorporated.
Add egg and yolk and whisk until the mixture is smooth with no sugar lumps remaining, about 30 seconds. Let mixture stand 3 minutes, then whisk for 30 seconds. Repeat the process of resting and whisking 2 more times until the mixture is thick, smooth, and shiny.
Using a rubber spatula or wooden spoon, stir in flour mixture until just combined, about 1 minute.
Stir in M&M’s and pretzels, giving the dough a final stir to ensure no flour pockets remain.
SCOOP COOKIES:
Divide the dough into 16 portions, each about 3 tablespoons (or use #24 cookie scoop).
Roll the dough into balls and arrange the dough balls 2 inches apart on the prepared baking sheets, with 8 dough balls per sheet. (Smaller baking sheets can be used, but will require 3 batches.)
BAKE, COOL, AND SERVE:
Bake cookies 1 tray at a time until cookies are golden brown and still puffy, and edges have begun to set, but centers are still soft, 10 to 14 minutes, rotating the baking sheet halfway through baking.