Heat your oven to 160°C Fan/180°C/355°F/Gas Mark 4.
Cut out two large pieces of greaseproof (parchment) paper, that are about 2 inches larger than the size of your Swiss roll tin or baking tray and set aside.
Sift your flour and baking powder together and set aside.
Separate your eggs and add the yolks to one mixing bowl and the whites to another, preferably metal or glass, mixing bowl.
With the whisk attachment fitted start beating your egg whites on a slow setting until they start to turn frothy. Then turn up the speed and beat until they form stiff peaks that stand up without falling back on themselves. This can take a couple of minutes to achieve. Set aside.
Clean the whisk off and then beat your egg yolks and sugar until they form a pale yellow thick paste, this can take a few minutes. Small bubbles should appear on the surface when ready,
Add your vanilla bean paste (or vanilla extract) and your buttermilk and beat in on a medium setting until just combined.
Add your sifted flour and baking powder mixture and beat in on a low setting. Scrape the sides and base of your bowl with your spatula to ensure all of the mixture is incorporated.
Add your beaten egg whites and gently fold them in using a large metal spoon. Stop as soon as no whites remain, overmixing will deplete the air that has been beaten into the eggs and result in a flatter Swiss roll.
Remove your swiss roll tin from your freezer and pour over your Swiss roll cake batter, spread out with the back of a spoon or knife to give an even surface.
Bake in the centre of your preheated oven for 10-12 minutes. The Swiss roll is ready if the centre bounces back when gently pressed and the cake is golden all over.
When your Swiss roll is baked run a knife around the edge to ensure the cake has not stuck to the sides of the tin.
Place one of the large pieces of greaseproof (parchment) paper which you cut out earlier over your cake and flip the cake over so that it sits on your new piece of paper.
Starting at the top short end, carefully peel the greaseproof paper off your Swiss roll.
Take your remaining large piece of greaseproof paper and lay it over the swiss roll, place a large baking in on it and flip the cake over, so that the patterned side is now face down.
Next, starting at the short end nearest to you start to tightly roll your cake up, keeping both pieces of greaseproof paper within the roll as you roll it up.
Leave your rolled up Swiss roll to cool fully at room temperature.