In a heatproof bowl, combine chopped dark chocolate and coconut oil. Melt using a double boiler or microwave on low heat until smooth and glossy.

Using a brush, coat a silicone dome mold with the melted chocolate for even coverage. Refrigerate for 15 minutes until set.

Apply a second layer of melted chocolate to reinforce the shell, then chill for another 15 minutes until solid.

Pour heavy cream into a medium bowl and whip until soft peaks form, about 3-5 minutes.

Mix mascarpone cheese, powdered sugar, and vanilla extract in a separate bowl until smooth.

Gently fold whipped cream into the mascarpone mixture until just combined.

Un-mold the chocolate shells and fill each dome with the mascarpone mixture, smoothing the tops.

Seal domes by pouring melted chocolate over filling if desired, then chill for 1 hour.

After chilling, un-mold domes onto serving plates and dust with cocoa powder before serving.