In a saucepan, add blueberries, sugar, and milk. Heat up the mixture until it just starts to bubble then shut off the heat.
Sprinkle in gelatin powder and stir until it has been dissolved.
Then, quickly blitz it in a food processor or blender until it is smooth. Let it cool while you whip your cream.
Whip your cold cream in a mixing bowl until it turns into soft cream. Do not whip until it turns stiff peaks.
Then, drizzle in yogurt, lemon juice and zest of the lemon skin. The mixture will thickens up as you fold.
Finally, stir in blueberry mixture that has been cooled slightly and milk until evenly combined.
Prepare a 16CM round cake ring along with a 6CM transparent plastic cake wrapper to layer the cake.
Quickly, transfer one sponge cake into the ring as the base of the cake, then pour about half of the blueberry cream mixture into it until it covers the sponge cake and the sides.
Then, layer it with another sponge cake before adding the rest of the cream over to cover it up.
Roughly flatten the top with a spatula before letting it set up overnight in the fridge.