Just because something's your favorite doesn't mean that it can't be improved upon. The Beatles woulda been better had Magical Mystery Tour never appeared in their catalogue. Any given bathtub could be improved by making it just an inch deeper. My wife could improve by... er, on second thought, better not go there. But you get the idea.

Likewise, Twix—the classic caramel-topped, milk chocolate-covered shortbread cookies—have always been my favorite candy bar, but it's easy to see where there's room for improvement. The shortbread is crisp enough to do its job, but it could have a more robust flavor and more short (i.e., crumbly) texture. The caramel layer could benefit from the addition of real butter instead of the flavorless palm oil you'll find on the ingredients list. And then there's the chocolate. Not that I don't appreciate Mars' super-sweet milk chocolate, but wouldn't it be nice if that cookie and caramel could come enrobed in, shall we say, the more adult flavor of high quality dark chocolate?

That was my goal this holiday season: a cookie that packs in everything I love about Twix, but with higher quality, more flavorful ingredients. Twix, v2.0 if you will.

The Cookie

Of course, Twix didn't invent this flavor combination. In bar-form, it's known as Millionaire's shortbread, though this variation produces individual round cookies—a much more elegant approach for the holidays, I believe.

First step: improving the cookie. Classic twix are made with a shortbread biscuit that is not much more than sugar, wheat flour, and palm oil. For my version, I knew I wanted something with a little more flavor. This buttery short bread recipe I developed for Cook's Illustrated (warning: pay wall) back in 2009 was a great place to start.

Rather than plain wheat flour, the dough incorporates some oatmeal that I grind to a fine powder in a blender or spice grinder, giving the finished shortbread a much more interesting flavor. A touch of cornstarch mixed into the dry ingredients also ensures that the cookies come out crisp and tender, rather than tough and dense.

It's a super simple dough to make: just combine the powdered oats, flour, cornstarch, confectioner's sugar, and a pinch of salt in a stand mixer, then beat in butter until it forms a cohesive dough.

Typically, you'd press the dough into a round pan with your fingers to shape it, but for these cookies, I figured rolling and cutting the dough out would work better. With a plain rolling pin, the soft dough ends up sticking and tearing. Instead, I rolled out the dough between sheets of parchment paper.

It's easy to get the dough out to a thin, even layer this way. I aimed for cookies about 3/16th of an inch thick. Seems pretty thin for a cookie—particularly a Twix imitator—right? But there's method to the madness.

Before I started, I figured there were two basic approaches to a caramel-filled cookie I could go with. The easier of the two is a thumbprint-style cookie, where you make a small ball of dough, then press it down in the center with your thumb, forming a well. This method is okay for casual cookies, but I wanted something that looked a little more refined on my holiday cookie spread.

The second method is better suited for that: filling them like linzer cookies.

With this technique, you cut out an even number of circles with a cookie cutter, then cut a smaller circle out of the center of half of them.

And while with classic linzer cookies you'd bake the circles and rings separately, filling and combining them after baking, I found it was much better to lay out the circles then top them with the rings before baking. (Be careful, those rings of dough are pretty delicate.)

By pressing down slightly on the rings, you end up with a completely solid shortbread cookie with a nice, deep, circular well in it (the scraps of leftover dough can be re-rolled to cut out more cookies). And because shortbread cookies are completely unleavened, they don't change their shape at all while baking. At least, I thought they wouldn't. In reality, they puffed up a bit in the center, ruining those wells I'd constructed. Docking them with a toothpick just before baking created channels for steam to escape, solving that problem.

I start the cookies in a hot 450°F oven, which gets them to begin to set before dropping the temperature to 300°F, which allows them to cook through completely until crisp and lightly golden brown.

The Caramel

Next up, the caramel filling. There are a number of different ways to make chewy caramel that stays soft at room temperature. The easiest by far is to simply buy some high quality caramel candies, microwave them in the oven until melted, then pour the melted caramel into the cookies. But that'd be cheating (I won't tell if you don't).

If you want to go from scratch, however, you've got two basic techniques. Both require a good thermometer. The first is the classic technique, in which you first make a sugar caramel by heating sugar, corn syrup (corn syrup is an invert sugar that helps prevent re-crystallization down the line), and water in a saucepan until it darkens in color. Once it hits the right shade, you whisk in some butter and heavy cream and reheat it to 245°F before stirring in some vanilla and pouring it into the cookies.

This method is a little finicky. First off, there's the crystallization problem. While the sugar is caramelizing, if you drop even a few specks of hard, crystallized sugar into the melted sugar (say, the sugar that's clinging to the edges of the pot), the entire pot will rapidly seize up, requiring you to start over again from scratch. It also requires you to use your thermometer twice, once during the caramelization, and once after adding the butter and cream.

A much easier, more foolproof, and—to my mind—tastier method is to utilize protein-packed, already-been-cooked sweetened condensed milk. With this method, all you have to do is combine the condensed milk, some sugar (I use a mix of white and brown), butter, corn syrup, and salt in a pot and heat it up to 245°F before stirring in some vanilla (adding the vanilla at the end keeps its flavor bright). No chance of crystallization, you only need to monitor the temperature once, and I actually really like the flavor condensed milk brings to it.

Once the caramel is made, I spoon it into the center of each cookie, letting it rise up above the edges a little bit. Any excess caramel can be set in a buttered casserole dish and cut into individual candies after cooling at room temperature for a couple hours.

The Chocolate

Once the caramel is set, we're at the last stage, and for this, I don't need to tell you twice that a good quality dark chocolate is what you're going to want to use.

In order to get your chocolate to set up with a nice glossy finish, melt-in-your-mouth-not-in-your-hand qualities, and a decisive snap, you'll need to temper it by melting it, then precisely controlling its cooling process to form the right type of crystal formation in the cocoa butter. I already spent many hours and about 5,000 words explaining the hows and whys of tempering chocolate so I won't bore you with the details here, but do read up on it if you're interested.

The short version? Melt your chocolate at 115°F, cool it to 85°F while adding some fresh, unmelted chocolate to it and stirring vigorously, then reheat it to 90°F. It should come out nice and pourable, which lets you do this:

Pour the chocolate over the cookies while they rest on a a wire cooling rack to allow the excess to drain off onto a sheet of parchment paper below. A few quick raps of the tray on the counter will get you a thin, even layer of chocolate over each cookie. Exactly what the doctor ordered.

I don't know about you, but I enjoy the flavor of good coarse salt with both chocolate and caramel, so it seems like a logical addition to these cookies before the chocolate solidifies (which, if it was tempered properly, should be just a matter of minutes).

Don't those look pretty?

I'm not really much of a sweet tooth, but it's pretty hard to keep your hands off of these when there's a whole plate of them on the table and you know what's hiding under that chocolate.

Make sure to make twice as many as you think you're gonna need, because just like Twix, these cookies are best enjoyed in pairs.

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