I love eating warm banana bread with cream cheese so this roll cake is like a fancy version of that. There's a sweet cream cheese filling and chopped walnuts sprinkled on the cake for a little bit of crunch.
Preheat the oven to 350oF, grease and line a 15 x 10 inch jelly roll pan with butter and baking paper.
In the bowl of a stand mixer, beat the eggs together with the whisk attachment. Gradually stream in the sugar whilst still whisking. Keep whisking until you get a thick, pale foam. Add the mashed banana and mix in briefly.
Add the flour, baking powder and salt then use a rubber spatula to gently fold together until combined.
Pour into the prepared pan and gently spread out into an even layer. Sprinkle with the chopped walnuts and bake for 10-15 minutes until dark and the cake springs back when gently poked.
Remove from the oven, flip out onto a clean tea towel dusted with powdered sugar. Starting at the short side, roll the cake up tightly into a log and leave to cool.
Beat the powdered sugar and butter together until smooth. Stir in the cream cheese and vanilla extract.
Fill the cake:
Gently unroll the cooled cake. Peel off the baking paper and cover with the filling. Re-roll into a log and serve immediately. Keep leftovers covered in the fridge for up to 5 days.