Preheat the oven to 180°C (356°F).
Mix almond flour, cocoa powder, and erythritol together.
Add coconut oil and almond milk, and make a dough.
Evenly spread the dough into a tart pan.
Bake for 10 minutes and let it cool.
Melt dark chocolate and unsweetened almond milk together using a double boiler.
Pour the chocolate filling into the tart and chill in the refrigerator for 2 hours.