Preheat the oven to 180°C and line a 24cm square cake tin with baking parchment.
Sift the flour, baking powder, bicarbonate of soda, cinnamon, and ginger into a bowl.
Gently heat the golden syrup, honey, and butter in a pan until melted.
Stir the muscovado sugar into the syrup mixture and allow it to cool slightly.
Halve or quarter the plums and remove the stones.
Whisk the eggs and milk together in a separate bowl.
Incorporate the syrup mixture and the egg mixture into the dry ingredients to form a loose batter.
Pour the batter into the tin, add the plums, and bake for 30-35 minutes.
Simmer the extra plums, sugar, butter, and ginger syrup in a covered pan until softened.
Serve the cake topped with the spicy plum mixture and double cream.