If the strawberries are large, cut them into smaller pieces, then combine all the ingredients in a saucepan.

Cook over low heat, stirring constantly, until the sugar has fully dissolved.

Increase the heat to high and boil the jam for 3 to 5 minutes.

Reduce to medium heat and simmer, stirring occasionally, until the jam has thickened.

Transfer to a container.

Let cool to room temperature, then refrigerate.

Make the vegan buttermilk by mixing the oat milk and vinegar.

Let it sit for a few minutes to curdle and thicken.

Whisk together all the dry ingredients in a large mixing bowl.

Add the vegan buttermilk and melted vegan butter to the dry ingredients, and whisk or beat with an electric mixer until smooth.

Preheat the oven to 170°C.

Line a baking tray with parchment paper, then pour in the batter.

Bake for 20-25 minutes.

Let the sponge cool completely before cutting.

Refrigerate if you don't need it right away.

In a saucepan, combine the oat milk, sugar, vanilla powder, and cornstarch, then whisk well until the cornstarch has fully dissolved.

Cook over medium heat, whisking constantly, until thickened.

Remove from the heat.

Add the cold butter, then strain to remove any lumps.

Cover directly with plastic wrap and keep at room temperature.

Make sure the pastry cream has cooled completely to room temperature.

Add the softened vegan butter to the vanilla pastry cream.

Beat it in a little at a time with a hand mixer or stand mixer until the mixture is light and smooth.

Divide the mousseline evenly between two bowls.

Add the strawberry jam to one half, then mix until smooth.

Cover and keep in a cool place, but not in the refrigerator.

Bring the water and sugar to a boil in a saucepan.

Remove from the heat and set aside.

Combine the cream and vanilla in a bowl, then whip to stiff peaks.

Refrigerate if you don't need it right away.

Cut out two round sponge layers.

Cut one to match the size of the cake ring (23 cm); the other should be slightly smaller so it fits inside the cake.

Prepare a 23 cm cake ring, 4 cm (1.5 in) deep, lined with an acetate strip.

Place the first sponge layer in the bottom, brush it with sugar syrup, then pipe the vanilla and strawberry mousselines alternately around the sides.

Press the piped mousseline against the ring, then smooth it upward to cover the entire ring.

Spread a layer of mousseline over the sponge.

Top with about 150 grams of strawberry jam.

Spread evenly with an offset spatula or the back of a spoon.

Place the second sponge layer in the center, brush it with sugar syrup, then spread mousseline over the top to fill the mold.

Remove any excess cream, then freeze for at least 1 hour.