Set a rack in the center of the oven and preheat to 350ºF (180ºC).
Finely pulse together ladyfingers, brown sugar and espresso powder in a food processor fitted with an 'S' blade. Then pulse in extra-virgin olive oil.
Transfer the crumbs to a 9-inch tart pan with a removable bottom. Using the bottom of a round measuring cup, firmly press the crumbs into the bottom and up the sides of the pan. Bake for 10 minutes and allow the crust to cool in the tart pan on a wire rack. If you are pressed for time, cool in the fridge for 30 minutes.
Add finely chopped chocolate to a medium bowl and set aside.
Heat cream in a small saucepan or microwave in 20 second intervals until simmering. Then pour hot cream over chocolate, making sure to completely submerge it. Let stand, untouched for 4 minutes and gently stir until combined.
Stir in room temperature butter.
Pour the filling into your tart shell and chill for 1 to 2 hours or for up to 3 days.
Add cold mascarpone cheese, powdered sugar and vanilla into a large bowl. With a hand-held mixer, whisk until combined.
With the mixer on medium/high speed, slowly add heavy cream to the mascarpone mixture and whisk until you get stiff peaks.
Transfer mascarpone topping to a piping bag fitted with a open tip or star tip or to a freezer bag with the tip cut off. Pipe the topping in a decorative pattern, sprinkle with cocoa powder and enjoy!
Store in an airtight container, in the fridge for up to 4 days.