Mix almond flour and cocoa powder together.
Add egg, erythritol, and unsweetened almond milk and knead into a dough.
Spread the dough into a tart pan.
Bake in a preheated oven at 180°C for 12 minutes.
Melt unsweetened dark chocolate and coconut oil together in a double boiler.
Pour the melted chocolate over the baked tart.
Chill in the refrigerator for 1 hour until set.