Make the Rum Caramel: In a medium saucepan, combine the 200g caster sugar and 125ml water. Bring to a boil over medium-high heat, stirring occasionally, until the sugar has dissolved. Continue to cook, without stirring, until the mixture turns a deep amber color, about 10-12 minutes. Remove from heat and carefully pour in the 130ml double cream (be careful, as it will bubble up). Stir in the 1½ tbsp dark rum and set aside.
Preheat the oven to 180°C fan. Grease a 20cm Bundt tin with butter and dust with flour.
In a large bowl, beat the 100g unsalted butter with the 70g caster sugar and 70g soft light brown sugar until light and fluffy. Beat in the 2 large eggs one at a time, then stir in the 1 tsp vanilla extract.
In a separate bowl, whisk together the 110g self-raising flour, 100g ground almonds, 2 tbsp malted milk powder, ⅛ tsp salt, ½ tsp ground cinnamon and ¾ tsp bicarbonate of soda.
Fold the dry ingredients into the wet ingredients, then fold in the 2–3 mashed ripe bananas (225g) and 100g soured cream. Finally, fold in the 2 tbsp dark rum.
Pour the batter into the prepared Bundt tin and bake for 45-50 minutes, until a skewer inserted into the center comes out clean. Allow to cool in the tin for 10 minutes, then turn out onto a wire rack to cool completely.
Drizzle the Rum Caramel over the top of the cake to serve.
