• Heat the oven to 250°F and adjust the oven rack to the middle position.

For the Chocolate Raspberry Filling:

• Place the chopped chocolate in a large bowl and set aside.
• In a saucepan set over medium-high heat, bring the cream, espresso powder, and salt to a simmer, stirring to dissolve.  Do not allow the cream to boil.  
• Remove the cream mixture from the heat and pour over the chopped chocolate, then cover with a lid or plate and let rest for 5 minutes.  When softened, stir with a spatula or spoon until combined and smooth. 
• Add the butter 2 or 3 pieces at a time, stirring until all the butter has been incorporated and the chocolate is smooth and shiny.  
• Pour the beaten eggs through a fine-mesh strainer into the chocolate, stirring until thoroughly blended.    
• Add the raspberry syrup and stir into the chocolate mixture.  
• Pour the chocolate filling into the pre-baked pastry crust, smoothing it level with a spatula.  Carefully bump the tart on the counter several times to remove any air bubbles.  Place the tart on a rimmed sheet pan and transfer to the oven.

Bake the Tart

• Bake the tart until the outer edge of the filling is set and faint cracks appear on the surface, about 40 to 45 minutes.  The filing will be very loose and will appear to be uncooked, that is just fine, as it will firm up as it cools.  
• Remove the tart from the oven and transfer to a wire cooling rack.  When fully set, transfer to the refrigerator to chill for 3 to 4 hours, preferably overnight. 

For the Raspberry Sauce

• Combine the frozen raspberries, water, lemon juice and sugar in a saucepan set over medium heat.  Bring to a low boil and cook while stirring occasionally and mashing the berries with a spoon or spatula for about 10 minutes. 
• In a small dish, stir the cornstarch and cold water together.  Temper the slurry with 2-3 tablespoons of the hot berry mixture and slowly stir into the saucepan of berries.  Continue to cook and stir for about 3 minutes until the sauce thickens.
• Transfer the sauce to a bowl and place it in the fridge until it is cool.

To Finish the Tart

• Remove the chilled tart from the refrigerator and spread 1 cup of the prepared raspberry sauce over the top, spreading to the crust edges.  (You will have approximately 1 cup of sauce left over to serve as extra sauce or use as an ice cream topping.)
• Arrange the raspberries on top of the tart.

To Serve: 

• Slice the tart into serving slices using a thin, sharp knife, dipping the knife into hot water and wiping dry with each slice.