Mix the biscuits with the melted butter and distribute the mixture along the bottom of a form. Put it in the fridge for the layer to cool.
Beat the mixture until you get a fluffy cream and pour it over the layer. Bake the cake at 338°F (170 °C) until fully ready. Once the dessert has cooled, leave it overnight in the fridge.
For the topping: Mix the thawed blueberries with the sugar, 1/4 cup water and the starch diluted in a little water.
Boil the mixture on low heat until thickened - about 5 min. Then remove it from the heat, add the lemon juice and stir.
Serve each piece with the prepared topping poured over it.