Preheat the oven to 160˚C/ Fan 140˚C/Gas 3. Grease a 23cm springform cake tin and line the base with baking parchment. Mix the rhubarb with the extra 2 heaped tbsp caster sugar and 1 tsp cinnamon; set aside.
In a large bowl, beat the remaining 225g sugar and 2 tsp ground cinnamon with the melted butter, eggs, vanilla and ginger. Mix in the flour, followed by the rhubarb, until everything is combined.
Pour the cake mixture into the tin and smooth the surface, making sure the batter is evenly distributed before scattering over the flaked almonds. Bake for about 1 hour 15 minutes, until a skewer inserted into the centre comes out clean; cover with foil after 1 hour if it starts to brown too much. Leave to cool in the tin.
When you are ready to serve, whisk the cream with the icing sugar, cinnamon and vanilla to soft, light, pillowy peaks. Serve each slice of cake with a generous dollop of the cinnamon cream on the side.