Layered Chocolate Mint Bars

Preparation

1. Step 1

   Heat the oven to 325 degrees with a rack in the middle position. Line a 9-by-13-inch baking dish with two sheets of aluminum foil, allowing them to extend past the rim of the pan on all sides. (This will help you remove the mint bar from the pan when you’re ready to serve.)

2. Step 2

   To make the crust, whisk together the flour, sugar, cocoa and salt in a large bowl. Add the cubed butter and mix with your hands, pinching the butter in, until it forms a crumbly, sandy texture. Transfer the mixture to the lined pan and spread it out into an even layer that completely covers the bottom of the pan. Pack the mixture down firmly so it’s as smooth and flat as possible. Bake until dry-looking and set, about 25 minutes. (A few little cracks in the crust won’t matter.) Place the baking pan on a wire rack to cool for 10 minutes, then transfer to the fridge to chill.

3. Step 3

   Next, make the dark chocolate ganache: combine the cream, mint, vanilla and salt in a large saucepan. Heat the mixture over high until it comes to a strong, rolling boil. (Boiling is crucial in order for the ganache layers to set properly.) Turn off the heat, cover and let the mixture steep for 10 minutes.

4. Step 4

   Meanwhile, place the chocolate chips in a large mixing bowl and set a mesh strainer over top. When the cream mixture has steeped, pour it through the strainer onto the chocolate. Using a stiff spatula or the back of a large spoon, press as much liquid as possible out of the mint leaves (discard the leaves). Let stand for 3 minutes, and then whisk until smooth. Add the butter and whisk until incorporated.

5. Step 5

   Pour half of the dark chocolate ganache (about 1¾ cups) onto the chilled crust, smoothing it out with an offset spatula into an even layer to the edges of the pan. Give the pan a few gentle taps on the counter to even out the ganache. Return to the fridge and chill for 45 minutes, until the dark chocolate layer is firmed up and set (it may not be rock-hard).

6. Step 6

   When the first layer has been chilling for 30 minutes, melt the white chocolate in a medium heatproof bowl over a gently simmering double boiler (or in 10-second intervals in the microwave, stirring between intervals). Add the crème de menthe all at once and whisk vigorously until smooth and incorporated. (The mixture may separate a bit at first, which is OK.) Set aside to cool to room temperature, 5 to 10 minutes. (It should be cooled yet still pourable for the next step. Otherwise, it will begin to re-melt the dark chocolate layer.)

7. Step 7

   When the dark chocolate layer is firm and the white chocolate is cool, give the white chocolate mixture a vigorous stir and then drizzle evenly over the dark chocolate. Working quickly so it doesn’t set, smooth it out with an offset spatula into an even layer to completely cover the dark chocolate. Immediately give the remaining dark chocolate ganache a whisk to smooth it out again, then pour on top in an even layer, gently smoothing it out to completely cover the white chocolate. (If the white chocolate mixture or remaining dark chocolate ganache are no longer pourable, feel free to reheat briefly over the double boiler while whisking a bit.)

8. Step 8

   Give the baking dish a gentle tap on the counter as before and transfer back to the fridge to chill overnight (or up to 5 days), covering in plastic wrap after the chocolate has fully set.

9. Step 9

   When ready to serve, gently pull up on opposite sides of the foil and place the mint bar on a cutting board. Slice into 2-by-1-inch rectangles for a perfect little after-dinner bite, or cut it into large candy bar-size rectangles for an even more indulgent dessert. For the cleanest cuts, dip a sharp chef's knife in hot water and wipe it dry on a clean dish towel between each cut. Serve chilled. If not enjoying immediately, keep the bars covered in plastic in the fridge for up to 1 week or freeze for up to 3 months.