Preheat the oven to 350°F (175°C). In a bowl, mix flour, cocoa powder, and sugar. Cut in cold butter until crumbly. Press into a tart pan evenly across the bottom and sides.

Bake the crust for 15 minutes until firm. Let cool.

In a saucepan over medium heat, combine heavy cream and chopped dark chocolate. Stir until smooth.

Whisk eggs in another bowl until frothy. Gradually add the chocolate mixture while whisking to prevent scrambling.

Pour the filling into the cooled crust and smooth it out.

Bake for another 20-25 minutes until set but slightly wobbly in the center. Cool completely before slicing.