In a mixing bowl, cream together butter, shortening, peanut butter, 1/2 cup granulated sugar, and brown sugar until light and fluffy, about 2 minutes.: You will notice the mixture lighten in color and become aerated, which creates tiny pockets of air that help the cookies rise slightly and develop a tender crumb. The aroma at this stage is rich and slightly caramelized from the brown sugar mingling with the peanut butter , and you should hear a faint buzz from the mixer as it works the fats into a smooth, glossy texture. If the fats are too cold, the mixture will look lumpy and will not incorporate air, producing dense cookies, so allow the unsalted butter and vegetable shortening to soften beforehand. A common pitfall is overcreaming, which can make the dough too soft and cause excessive spreading in the oven, so stop once the mixture is light and fluffy.
Add eggs, mixing after each addition. Mix in the vanilla.: When you add the eggs , the batter will become silkier and slightly more fluid, and the mixer will sound smoother. Adding eggs one at a time ensures they emulsify properly, which stabilizes the dough and gives a uniform structure. The scent of vanilla extract lifts the deeper notes from the brown sugar and peanut butter . If you add cold eggs straight from the fridge, the fats can seize and the mixture may appear curdled, so bring eggs to room temperature or add them slowly while mixing. Avoid high speed once the eggs are incorporated, because that can over-aerate and weaken the dough.
In a separate bowl, whisk together flour, baking soda, and salt.: Whisking distributes the baking soda and salt evenly through the all purpose flour , so the cookies rise uniformly and the seasoning is balanced. You will see the dry mix lighten in color and form a homogenous powder, which makes folding into the wet ingredients predictable. If the flour contains lumps, break them up now to avoid pockets that do not hydrate, as those would create uneven texture. A common oversight is not measuring flour correctly, which leads to overly dry dough, so spoon and level for accuracy.
Stir dry ingredients into the wet ingredients and mix gently to combine. Don't over-mix. The dough will be very soft. Refrigerate for at least 30 minutes, or up to 3 days.: At this stage you will feel the dough transform from sticky batter to a cohesive, very soft mass. The surface will be slightly tacky, and the scent will be warm and nutty. Chilling firms the dough, allowing the fats to solidify and making the cookies easier to shape, which also controls spread during baking. Overmixing here develops gluten in the all purpose flour , resulting in tougher cookies, so fold just until no streaks of flour remain. If the dough seems too loose to form, a brief chill will make it manageable; if you skip chilling, expect more spreading in the oven.
Preheat oven to 375 degrees F.: Heating the oven to the right temperature ensures the exterior sets quickly while the interior stays soft, creating that desirable contrast. You should smell a faint warm, dry air from the preheated oven when you open it, and the heat helps the Rolo melt properly when placed on a freshly baked cookie. An oven running cool can lead to pale cookies that do not set, while too hot an oven will brown them too quickly, so use an oven thermometer if your oven is uncertain.
Line a cookie sheet with parchment paper.: The parchment provides a nonstick surface and helps cookies bake evenly across their bottom, preventing hot spots and making cleanup easier. You will notice the parchment retains a slight warm scent from the oven but nothing overpowering. Avoid greasing the sheet in addition to using parchment, as extra fat can cause additional spreading. If you skip parchment, rotate the sheet halfway through baking to avoid uneven browning.
Scoop dough into large balls and roll them into an oval shape. Place on prepared baking sheet. Bake for 9-12 minutes, until set and no longer glossy looking.: As the cookies bake, they will puff slightly and the edges will set first, creating a gentle ridge while the centers remain soft. Watch for the glossy sheen to disappear and for the bottoms to take on a hint of golden color, which indicates doneness without overbaking. You will hear a faint crackle as moisture leaves the cookie and see tiny steam vents on the surface. A common mistake is underbaking for a soft center that will collapse, so err on the side of fully set but not browned, and rotate the pan if your oven heats unevenly.
Remove from oven. Press pretzels into the top of the cookie, for the ears. Press a rolo into the center, for the nose. Add two candy eyes, or chocolate chips for the eyes. Place a dot of frosting in the center of the rolo to secure a red m&m candy on top, for the nose. Allow to cool on baking sheet, then transfer to cooling rack.: Right after the cookies come out you will see the surface sheen gone and the centers slightly domed, which is the perfect time to press in the decorations as the Rolo will soften and adhere. The contrast between the hot cookie and the melting caramel creates a warm, sticky bond that secures the nose. Adding a dot of decorating frosting anchors the red m m candies so they do not roll off later. If you wait too long and the Rolo cools, the candy will not stick, so work quickly but carefully. Transfer to a cooling rack once the cookies have set enough to move without distorting, and let them cool completely so the caramel firms and the pretzels stay crisp.