In a small bowl, beat together the egg yolk and vanilla extract.  Set aside in the refrigerator. Cut the butter into small pieces, set on a plate and place in the refrigerator as well until ready to use.

In the bowl of a food processor, using the metal “S” blade, add the flour, sugar, cocoa powder, and salt. Pulse to evenly distribute the dry ingredients.

Scatter the pieces of butter on top of the flour mixture. Pulse until each piece of butter is about the size of a pea.

Remove the lid and pour the egg mixture over the flour/butter mixture. Pulse until the dough just begins to come together. Remove the lid and (being careful of the blade) press a bit of the dough with your fingers to determine if it will stick together.  If not, sprinkle a teaspoon of cold water over the mixture, return the lid and pulse again to further combine the dough.

When the dough comes together, remove it from the processor bowl onto a clean counter. With the palm of your hand smear the dough away from you to incorporate. With a bench knife, gather up the pieces and smear again until incorporated. This simple technique is called fraisage.  It allows the dough to come together without using an excessive amount of liquid. Once the dough is in one mass, form it into a disk. Wrap it in plastic wrap and place in the refrigerator for at least an hour and up to 24 hours.

When ready to finish making the tarts preheat oven to 325°F and line a sheet pan with parchment paper. On a lightly floured board roll the pastry dough to a scant 1/8-inch thickness. Cut twelve 3 1/2-inch disks.  (The amount of dough for each disk is about 1 1/4 ounces.) On the parchment paper (to prevent dough from sticking) line each tart ring with a disk of dough. Chill the tart shells for at least an hour or until the dough is firm. Remove from the refrigerator, line the tart shells with parchment paper and fill with beans, rice, or pie weights and bake for 15 minutes.  Remove the weights and bake for an additional 5 to 10 minutes, or until the pastry looks dry and set.  The shells can be made up to 1 day ahead.

The caramel filling makes about 1 2/3 cups. You won’t need it all for this recipe.  Therefore, it can be cut in half.  But why would you want to do that when it can be refrigerated and drizzled on your favorite ice cream?

Have all of the ingredients measured out and at the ready as cooked caramel waits for no one.  In a medium heavy-bottomed saucepan add the water, sugar, and corn syrup and stir to combine.  Cook the mixture over medium-high heat, swirling the pan occasionally.  If necessary, brush down the sides of the pan with a pastry brush dipped in water. This prevents sugar crystals from falling back into the pan thus causing the mixture to seize. Cook until the caramel is dark amber, about 30 minutes.  Remove from the heat and carefully whisk in the butter, cream, and yogurt (the mixture will bubble up, so stand back), continue whisking until smooth.  (The caramel can be made up to 5 days in advance. Reheat in a microwave until it’s a pourable consistency.) Pour a bit of the warm caramel into each tart shell, filling about halfway. Let it sit for about 45 minutes to allow the caramel to set.

To make the ganache, place the chocolate in a medium bowl or glass measuring cup. In a small saucepan bring the cream just to a boil. (Don’t walk away as there’s nothing worse than cleaning up cream that has boiled over.) Pour the cream over the chocolate and let it sit for a couple of minutes. Stir and pour over the tarts.