In a food processor, add the dates, walnuts, oats/ buckwheat flakes and cacao powder. Blitz until combined and only small walnut chunks remain.
Split the mixture evenly between 2 tart tins. Press the mixture down and up the sides to create the base of the tarts, then place in the freezer to set for 30 minutes.
Meanwhile, in a saucepan over a medium heat, simmer the coconut milk, Baileys and dark chocolate melts until completely combined. Leave to cool.
Gently remove the bases from the tart tins and place on a baking tray.
Give the filling a stir to ensure it is still smooth with no lumps, then fill up the bases of the tarts.
Place back in the freezer to set for 45 minutes, before dusting with cacao powder.
Store in the freezer for up to 3 weeks, and allow 10-15 minutes to warm up before eating immediately.