Preheat the oven to fan-assisted 160C / 180C / 350F / gas 4 and grease and line two 20cm / 8 inch cake tins.
Mix the mashed plantains with the 2 eggs, oil and milk until well combined.
In a separate bowl, mix together the flour, sugar, cinnamon and baking powder. Add the wet ingredients to the dry ingredients and mix until well combined and lump free. Whisk the egg whites until just stiff and use a spatula to gently fold in the egg whites.
Split the cake mixture evenly between the two cake tins. Bake in the oven for about 30 mins, or until a skewer inserted into the cakes comes out clean. Remove the cakes from the oven, let cool in the tins for 5 mins before cooling completely on a wire rack.
You can eat one cake now and store one in the freezer till needed.
Seve plain or with some ice cream, whipped cream and fruits.