In a small, microwave-safe bowl, microwave the chocolate on high for 30 seconds. Stir and microwave for another 30 seconds, stirring until fully melted. Allow to cool for 10 minutes.

Beat together the cream cheese and butter on high until light and fluffy. Stir in the cooled chocolate and mix until well combined. Using a rubber spatula, scrape the bottom and sides of the bowl and stir once more. Add the flour and mix until just combined and it comes together to form a rough dough. Form into a disk and wrap in plastic. Chill for at least 1 hour.

For the filling, in a medium saucepan, combine the dark chocolate, corn syrup, sugar, butter, cocoa powder, espresso powder, and salt. Set over moderate heat and cook, stirring often, until melted through and mixture is smooth. Remove from heat and set aside to cool, about 10 minutes. Add the eggs, egg yolks, and vanilla extract and whisk until well combined, smooth and glossy.

Preheat oven to 350 degrees F.

Unwrap the chilled dough and place on a lightly floured work surface. Roll out into a large circle, about 1/4-inch thick. Transfer to a 10-inch removable bottom tart pan. Press the dough down onto the bottom and up the sides of the pan. Then press on the sides of the pan, using a rolling pin, to remove any excess hanging dough. Pour the filling into the crust and spread into an even layer. Cover the top completely with the walnuts. Place the tart onto a baking sheet and bake until the center has set, about 35 to 40 minutes. Remove from the oven and let cool completely. You can slice and serve at this point or wrap in plastic and chill until ready to eat. Tart can be kept in the fridge for up to 4 days. Enjoy!