Heat the blueberry purée and lemon juice to about 40°C. Add the pectin-sugar mixture, then bring to a boil, whisking constantly for about 3 minutes.
Pour immediately into the cake ring while still hot. Use a cake ring slightly smaller than the mold you will use for assembly. Let cool to room temperature, then freeze.
Raspberry Pastry Cream
Place the oat milk, sugar, vanilla powder, and cornstarch in a saucepan, then whisk until the cornstarch is fully dissolved.
Cook over medium heat, whisking constantly, until thickened. Remove from the heat.
Whisk in the cold butter, then strain to remove any lumps. Add the raspberry jam and mix until smooth. Cover and refrigerate until needed.
Prepare the Insert Ahead
Spread the raspberry pastry cream evenly over the frozen blueberry compote, then sprinkle the crushed graham-style crackers evenly over the top to form a layer.
Freeze for at least 2 hours, or until firm enough to assemble the cake.
Chocolate Sponge Cake
See the full recipe for the vegan gluten-free chocolate sponge here.
Use just one 1 cm-thick slice of sponge, and adjust the quantity accordingly.
White Chocolate Mousse
Melt the white chocolate with the vegan cream (50 g).
Whip the vegan cream (150 g), then fold it into the still-warm melted white chocolate.
Blackcurrant Mirror Glaze
Combine the NH pectin and sugar.
Heat the glucose, blackcurrant purée, water, and cream in a saucepan to about 40°C.
Add the pectin-sugar mixture, then bring to 102°C.
Transfer to a container and cover the surface with plastic wrap. Refrigerate.
Cake Assembly and Decoration
Prepare a silicone dome mold at least 4 cm deep. Spoon in the white chocolate mousse and spread it up the sides to coat the inside of the mold.
Press the frozen insert into the mousse, blueberry compote side down. Make sure the insert does not touch the bottom of the mold.
Place the chocolate sponge on top to seal the entremet. Freeze for at least 12 hours, or overnight.
Warm the blackcurrant glaze to about 50°C. Unmold the frozen entremet and place it on a wire rack. Spread the warm glaze over the top and smooth the surface with a spatula. Place a tray or plate under the rack to catch the drips.
Transfer the entremet to a cake board. Decorate with sliced berries and mint arranged in a pattern. See the video for details.
Let the entremet thaw in the refrigerator for 3-5 hours, making sure it is fully defrosted before serving.