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1
Sift together the flour and salt and set aside. In the bowl of a standing mixer with a paddle attachment, beat the butter for 1 minute. Then add the sugar and beat until light and fluffy, 2 more minutes. Beat in the egg yolk, just until fully incorporated.
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2
Add in the flour mixture and beat just until everything comes together into a dough - add the cream if the mixture is too dry. Do not overbeat. Scoop the dough pieces together and press them into a ball, then flatten this into a disc about an inch thick. Wrap with plastic wrap and refrigerate for an hour.
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3
Remove the dough from the refrigerator and let stand at room temperature for 5 minutes. On a lightly floured surface, roll the dough out into a circle about 1/8th of an inch thick. This dough can be a little delicate and tricky (which can be frustrating, but the baked shell gives you great flavor and texture). Use moistened fingers to repair any cracks. Gently drape your dough over a 9 inch tart pan with removable bottom (many pastry chefs recommend using your rolling pin to help with the transfer, but I never find this to help much, so I just lift it gently with my hands all the way underneath). Press the dough into the pan and trim the rough edges off. Freeze for 30 minutes.
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4
Preheat your oven to 350F. Prick the bottom of the tart shell all over with a fork. Put your tart shell on a baking sheet and place on the center rack in your oven. This pastry crust does not need to be lined and weighted because you want it to be able to breath and get a little crisped. Bake until golden brown, about 20-25 minutes in my oven. If the bottom of the tart has puffed up at all, just gently press it back down with a spoon. Remove and allow to cool to room temperature.
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5
Coarsely crush (you want them cracked into smallish pieces, but not anywhere near as small as if they were ground) the coffee beans using a mortar and pestle or a heavy pan. In a saucepan combine the crushed beans, the lemon zest, and 1 1/2 cups heavy cream. Bring just to a simmer, then remove from the heat and allow to sit for 15 minutes to infuse. Then strain the infused cream through a very fine strainer to remove any particles.
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6
While the cream is infusing, you should have time to make the ganache. In a very small saucepan, bring 1/4 cup heavy cream just to a boil. Remove from the heat and stir in the chopped chocolate. Allow to sit for 30 seconds to a minute, then using a wooden spoon or whisk, start stirring in small circles in the center of the saucepan slowly working your way out until you have a uniform melted ganache mixture (this stirring technique keeps it smooth and introduces a minimal amount of air). Pour the ganache into the cooked tart shell, spread it evenly over the bottom, and allow it to cool completely to room temperature.
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7
Go back to making the rest of the filling. In a small bowl, whisk the egg yolks for a minute until lightened and lemon colored. Over medium-low heat, combine the infused cream with the brown sugar in a saucepan, stirring until the sugar is completely melted. Bring the cream to a simmer, then take off the heat.
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8
Pour about 1/4 cup of the hot cream mixture into the egg yolks, whisking vigorously all the while to temper the yolks. Repeat. Then, scrape the egg yolk mix into the saucepan. Cook slowly over low, stirring constantly, until the custard is thick enough to coat the spoon and the spoon leaves a trail. (Patience young grasshopper. Slow is the key to smoothness.)
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9
Pour through a strainer into a bowl, put plastic wrap directly on the top and put in the refrigerator to cool for an hour.
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10
After an hour, whip the remaining 1/2 cup cream until almost stiff peaks form. Gently fold the whipped cream into the lemon-espresso custard mixture until fully incorporated. Spread this filling into the prepared tart crust. Cover the tart with plastic wrap and chill for 2 hours before serving.
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11
Phew. You have earned yourself a rather large slice, my friend!
