Preheat the oven to 180°C (160°C fan). Grease a 10 × 7.5 × 5 cm pan and line a 26 × 20 × 2.5 cm tray with greaseproof paper.
Mix the plant-based drink and apple cider vinegar; set aside 10 minutes to make vegan buttermilk. n a bowl, combine the gluten-free flour, baking powder, baking soda, arrowroot, and salt.
Cream the vegan butter and sugar until smooth, then mix in the fruit purée and vanilla. Add the dry ingredients and buttermilk gradually, whisking just until a smooth batter forms.
Spread the batter in the lined tray and bake for ~35 minutes, until a skewer comes out clean. Cool in the tray for 5 minutes, then transfer to a rack.
Brew 1 cup strong coffee (you won’t need all of it). In a clean bowl, whisk all filling ingredients until smooth; sweeten with maple to taste. Chill.
Trim the sponge edges and cut into 16 strips, then halve each strip lengthways to make 32 sponge fingers. Brush one side of each sponge finger with coffee (don’t soak). Lay a layer of sponge in your dish, top with coconut filling, add another layer of coffee-brushed sponge, and finish with the remaining filling. Cover and chill for 4 hours or overnight.
Dust with raw cacao and grated chocolate, slice, and serve.
