Make the vegan buttermilk: combine the oat milk and lemon juice. Let stand for 10 minutes, until slightly curdled or thickened.

Combine and sift the dry ingredients, except the sugar, into a mixing bowl.

Add the vegan buttermilk, olive oil, and sugar, then beat with an electric mixer until smooth and lump-free.

Preheat the oven to 170°C and line a flat baking tray with parchment paper.

Spread the batter about 1 cm thick on the lined tray and bake for 15-17 minutes.

Let the sponge cool completely before cutting.

Bring the agar-agar cream to a quick boil: in a small saucepan, combine the heavy cream, maple syrup, and agar-agar powder. Cook, whisking constantly, until it comes to a boil. Note: agar-agar sets quickly and can cause the cream to curdle; use an immersion blender to smooth it out and keep it warm. Set aside.

Melt the white chocolate: place the vegan white chocolate in a bowl and melt it over a double boiler or in the microwave. Set aside and keep warm.

Whip the lactose-free cream: in a bowl, whip the lactose-free heavy cream until soft peaks form. Set aside at room temperature.

Mix and fold in: gently warm the pumpkin puree in the microwave until just lukewarm, not hot. Add the melted white chocolate and the cream-agar mixture, both lukewarm, then mix well. Fold in the whipped cream until smooth and creamy. Set aside and keep warm while you assemble the cake.

Prepare the coffee-cream mixture: dissolve the coffee granules in the heavy cream. Bring just to a boil, then immediately remove from the heat.

Melt the dark chocolate: melt the chocolate over a double boiler.

Whip the lactose-free cream: in a bowl, whip the lactose-free heavy cream until soft peaks form. Set aside at room temperature.

Mix: combine the lukewarm coffee-cream mixture with the lukewarm melted chocolate. Gently fold in the whipped cream until you have a mousse with a slightly fluid consistency. Set aside and keep warm while you assemble the cake.

Prepare a cylinder of cake acetate 18 cm in diameter and 12 cm high. Make sure the ends are securely taped together.

Use a pastry ring or paring knife to cut out two sponge discs. One should be the same diameter as the acetate, while the other should be slightly smaller, leaving a gap around the edges.

Chocolate sponge layer: place the first chocolate sponge disc in the bottom, then brush it with coffee syrup.

Pumpkin cream layer: pour the pumpkin-white chocolate cream over the sponge. Smooth with a spatula if needed.

Coffee-chocolate mousse layer: place the second sponge disc in the center on top of the pumpkin cream, then brush it with coffee syrup. Pour the coffee-chocolate mousse over it. The mousse should be slightly warm and fluid enough to fill the narrow gap between the sponge and the acetate.

Refrigerate the assembled cake for at least 3-5 hours, preferably overnight, so the layers can set and firm up.

Before slicing and serving, dust the top with cocoa powder, then remove the acetate. You can also add grated dark chocolate or toasted pumpkin seeds for extra texture.