Preheat oven to 200°C. Grease a 25cm x 30cm Swiss roll pan.
Line with baking paper.
Dust lightly with flour.
Using an electric mixer, beat eggs and sugar together for 5 minutes or until thick and creamy.
Using a large metal spoon, fold flour into egg mixture until just combined.
Spread mixture over prepared pan. Smooth surface. B
ake for 5 minutes or until a skewer inserted into the centre comes out clean.
Turn sponge onto a sheet of baking paper.
Carefully peel away baking paper lining. Allow to cool.
Mash bananas roughly with a fork. Add icing sugar and stir to combine. Fold banana mixture into mascarpone.
Spread mixture over sponge, leaving a 1cm border.
Using baking paper as a guide, roll up sponge from short end to enclose filling.
Place sponge, seam side down, on a plate. Top with crushed pistachios. Dust with icing sugar. Serve.