It is worth investing in one of these (can find one for $10-15) if you plan on making this often as it makes it easy to remove the tart once its baked. Otherwise just make it in whatever round pan you have. The first piece will probably be difficult to remove but you should be ok after that. So lets begin:
Ingredients for the crust:
8tbs (1 stick) unsalted, melted butter
1/4 cup sugar
1/8 tsp salt
3/4 tsp pure vanilla extract
1 cup all-purpose flour
Ingredients for the filling:
3 tbs unsalted butter, cut into chunks
1/2 cup sugar
1/4 cup unsweetened cocoa powder
1 cup heavy cream
11/4 tsp instant espresso powder or instant coffee crystals
1/2 tsp pure vanilla extract
1 large egg, lightly beaten
Preheat oven to 350oF
Mix the butter, sugar, and vanilla in a bowl to make the crust. Add the flour and mix till well blended. The dough may seem too soft but this is fine. Press it evenly and thinly onto the bottom and sides of the pan
Bake for 20 to 25 minutes or until the crust is a golden brown
In the meantime start to make the filling. Place the butter, sugar, cocoa powder, and cream in a medium saucepan over medium heat. Stir until the mixture is blended, smooth and begins to simmer around the edges. Remove from heat and stir in the instant espresso or coffee powder and vanilla.
Just before the crust is ready, whisk the egg thoroughly into the hot choclate mixture. Pour the filling into the hot crust.
Place the pan into the over and turn the oven off (yes, off). Leave the tart in the over till it quivers like Jell-O. The recipe says this will take 10 to 12 minutes but I've found that it needs more like 20 minutes.
Let cool on a rack and serve at room temperature.
The coffee flavor is pretty mild in this tart so its great for those who don't particularly like coffee. Enjoy!