Size Matters: Reese's Pieces-Stuffed Cups, Regular vs. Big Cup

The Allure of the Tender Crunch
You see it in the Napoleon.  You see it in Sugar-Creme Wafers; in baklava, in Charms Blow Pops, and in extra-crispy fried chicken.  Humans love the sensation of breaking through a crunchy shell, or through multiple layers of crunch, in order to reach a tender treasure inside.  It may not be the pleasantest task to inquire as to why: perhaps some predatory common ancestor was given an evolutionary edge by enjoying the intermingling of crunchy bones with succulent meat, and one less impediment to high-protein nourishment led to differential reproductive success. Whatever the case may have been, today even vegetarians and vegans can indulge this desire for conflicting textures, and its persistence doubtless explains the appearance on the market of Reese's Peanut Butter Cups stuffed with crunchy Reese's Pieces.  Crucially, these are available in two sizes, the traditional petite size and a fattened up "Big Cup", and we'll discover that this actually produces two very different tastes.

There they stand, clothed in chocolate armor but vulnerable to the inevitable crushing chomp.

Peanut Butter Inside of Peanut Butter?
It's easy enough to accept the appeal of crunchy nuggets inside of peanut-butter cups, but it seems only natural to wonder why the filling should also be peanut-butter based.  Why not chocolate pieces, or crunchy rice, or pretzels?  Isn't peanut butter redundant?  I asked this question myself and it drove me to answer once and for all a question that has always bugged me: is the peanut butter filling inside Reese's Pieces the same as what's inside the peanut butter cup?  They'd always tasted different to me, but I wondered if that was because of the influence of the shell's distinct flavor and texture.  To be sure, the shell would have to be removed and the peanut butter within tasted on its own.  The process of doing this is tasty enough to undertake, albeit a little offputting to describe; the shelled candies just need to be popped into the mouth and gently sucked upon like a fragile hard candy until only tender nibs of peanut filling remain.

The briefest of visual inspections suggests that the filling in Reese's Pieces is distinct from that of their peanut butter cups.  The cup filling is coarse, grainy, even a little sandy.  The contours of the pieces are tight and crisp, their surface smooth and refined, suggesting almost a peanut-flavored white chocolate. And that's basically what they are.

As the photo above shows, the two fillings look very different, and the taste reflects this.  The cup contains a loosely packed peanut-butter fudge, sandy, salty, and nutty, reflecting the copious presence of coarse-ground peanut butter.  The pieces taste more like chocolate, al dente to the first bite 
but gradually softening in the warmth of the mouth and melting away smoothly.  This answers the question of why Reese's would put their pieces inside of their peanut-butter filling.  It introduces yet another texture into the mix, bringing the taste count to four.  First you have the milk chocolate, then peanut-butter filling, then the crunchy shell, and finally the smooth, almost chocolatey pieces.  Wheels within peanut-butter wheels.

Why the Big Cup Wins
This ambitious flavor and texture packing scheme does succeed, but with an important caveat.  If you run out to the drugstore and just pick up the regular-size peanut-butter cups with the pieces inside, you'll be sorely disappointed because there isn't enough room inside a standard-issue peanut-butter cup for all of this interplay of parts to be contained.  Even though the Reese's Pieces are miniaturized for this hybrid candy, they're still too large to easily fit within the chocolate shell, and so you'll find very few whole pieces in the small-size cups. Mainly you get sherds and slivers of shell, but few identifiable remains.  The interior of the normal-size cups looks like a careless archaeological dig of a ransacked city, all tiny scraps and fragments with no intact objects.

The compressed space inside a normally-sized Reese's cup leaves no room for Reese's Pieces to fit, whereas the roomy interior of the big cup allows the different elements to arrange themselves harmoniously.

The Big Cup is much better designed for the task at hand.  Like a practical minivan, it has plenty of room for all the critical passengers.  The peanut-butter filling piles up light and fluffy, the milk chocolate retreats to the outer edges and plays a supporting role while numerous little gems of crunchy, melty peanut-butter candy sit nestled inside, ready for the Mixmaster that is the human mouth to tumble them all together, crunchy meeting creamy, sandy swimming with smooth, as somewhere deep within us, our tree-swinging simian ancestor smiles.

On the left side, you see a very rare occurrence: an intact Reese's Piece within one of the small cups.  On the right, you see that multiple sightings of these full pieces are common in the Big Cup.  You can also see from this cross-sectional view just how dramatic is the texture difference between the smooth and refined filling of the pieces and the almost gravelly filling that's traditionally present in the cups.

Conclusions
Pieces within the cups are a big idea and they require a big canvas for their execution.  These Reese's Pieces-filled Big Cups may cost extra money, but it's go big or go home.