Place all ingredients into a medium bowl, except the milk.
Whisk with an electric beater.
Add the milk until a spreadable consistency is achieved.
Cover and set aside.
Grease a Swiss roll tray and line with baking paper.
Preheat the oven to 180◦C.
Beat the eggs and sugar with an electric beater until pale.
Fold the flour into the egg mixture with a spatula.
Spread evenly onto the prepared tray.
Bake 8 to 10 minutes. Start 8min timer
While roulade is baking, place a tea towel on the work surface. Cover the tea towel with a large sheet of baking paper and sprinkle with remaining castor sugar.
Turn the cake onto the baking paper once baked.
Roll the cake up from the short side, rolling the paper inside the cake.
Cool for 5 minutes, then unroll and allow to cool.
Spread with mascarpone buttercream filling and place raspberries on top of filling. Roll up the sponge cake, placing the end under the roll.