Preheat oven to 350°F. Line 2 cookie sheets with parchment papers or silicone baking mats.: The kitchen fills with a faint warm, toasty scent as the oven comes up to temperature, and that steady heat is vital so the cookies bake evenly. Preparing two sheets at once saves time and prevents crowding, which keeps cookies from merging. Make sure the parchment is flat and the mats lie smooth, because uneven surfaces create lopsided cookies. A common mistake is skipping the liner, which can lead to sticking and imperfect bottoms, so always prepare your pans first.
Stir together peanut butter, both sugars, and egg.: As you mix, notice how the glossy peanut butter softens and the sugars dissolve into it, forming a thick, cohesive batter with a sweet, nutty aroma. The sound is a gentle scraping as the bowl clears and the dough comes together. I use a sturdy spoon or spatula to fold until no streaks of sugar remain, which ensures even sweetness and texture. If the mixture seems too dry, small adjustments help, but be careful not to overwork the batter, as that can make the cookies tough. Avoid mixing at high speed, which can incorporate excess air and change the final texture.
Scoop cookie dough in desired size (I used a large ice cream scoop that's about 1/4 cup). Place a peanut butter cup in the center and roll to cover completely. The dough is pretty wet, so spray your hands with cooking spray so it doesn't stick.: The dough will feel soft and slightly tacky, almost spreadable, and the motion of scooping should be smooth and satisfying. When you tuck a peanut butter cup into the center and roll it in, the candy should be fully enveloped so it does not leak during baking. Spraying hands or lightly flouring them prevents the dough from clinging, which keeps shapes uniform. A trap I often see is making the ball too loose so the candy peeks out, which can melt onto the pan, so be generous when sealing the dough around the candy.
Place on prepared cookie sheet (3 inches apart) and top with 4-6 peanut butter M&Ms.: Arrange each dough ball with enough space to allow for gentle spreading, and the visual of bright M&Ms pressed into the top is cheerful. Pressing the candies in just enough to nestle them on the surface helps them stay attached during baking and creates a pleasing mosaic once baked. The sound is quiet as the candies lightly settle into the dough, and the contrast of color against the tan dough is attractive. Avoid crowding the pan, as that reduces browning and makes cookies stick together.
Bake for 10-15 minutes, or until they are just no longer glossy. Cool completely before removing from cookie sheet.: As the cookies bake, the kitchen will smell richly of roasted nuts and warm sugar, and the surface will shift from glossy to matte indicating doneness. Edges may firm slightly while centers remain soft, which is exactly what you want. Let the cookies sit on the sheet to finish setting, because removing them too soon can cause them to break. A typical error is overbaking until they look dark, which removes the tender interior, so pull them when the gloss fades and allow residual heat to finish the bake while cooling.