Combine plant milk and lemon juice in a small bowl. Let sit for 5 minutes until slightly curdled. Set aside.

Preheat oven to 140°C. Line a 22cm springform cake tin with baking paper and dust with cocoa powder (instead of flour for better flavor).

Place chocolate and vegan butter in a heatproof bowl set over a saucepan of barely simmering water. Stir occasionally with a spatula until melted and combined. Ensure water doesn't touch the bowl bottom and heat remains gentle. Set aside to cool slightly.

In the bowl of an electric mixer fitted with whisk attachment, combine aquafaba, cream of tartar, brown sugar, and golden syrup. Beat on high speed for 10-12 minutes until very thick, fluffy, and tripled in volume. The mixture should hold firm peaks and have a glossy appearance.

Turn mixer off and pour the slightly cooled chocolate mixture straight into the aquafaba sabayon. Add almond meal, flour, vegan buttermilk, vanilla, and salt.

Return bowl to mixer and use the lowest speed to gently combine all ingredients (mimicking hand-folding). The mixture will be streaky as the aquafaba foam mingles with chocolate ribbons. Stop the whisk just before the last streak disappears - this ensures a light batter that hasn't been overworked.

Remove bowl from mixer and use spatula to scrape base of bowl, ensuring any settled chocolate is well combined.

Pour batter into prepared tin and bake for 45 minutes until top forms a crust.

Remove from oven and cover with frozen raspberries, gently pressing them into the surface (don't add them before initial baking or they'll sink).

Return to oven for 30-40 minutes until center is springy to touch. The center will remain beautifully gooey - this is correct! If raspberries start browning too much, cover with foil.

Let cake cool in tin for at least 2 hours before removing. For clean cuts, heat knife blade in hot water and wipe dry between slices.