Melt the chocolate in a thin-sided bowl over a gently simmering bain-marie, stir until smooth, then stir in the coconut oil and salt. Using a teaspoon, pour a little chocolate onto the blueberries, stick clusters of 3-5 berries together, place on a baking tray and freeze for approx. 10 mins. Using a fork, dip the individual clusters into the remaining chocolate, place them side by side on a piece of baking paper, sprinkle the coconut flakes over them and cool them for approx. 15 minutes before eating.