For the strawberry filling, put a third of the strawberries in a blender or food processor with the granulated sugar and blend well. Transfer the strawberries to a bowl and add the Marsala or orange juice. Stir in the remaining strawberries and chill in the fridge. (The flavour gets better the longer you leave it, so do this a few hours ahead if you can, though if you are ready to go now then a minimum of 30 minutes is fine.)
Meanwhile, for the sponge, preheat the oven to 190C/375F/Gas 5. Grease and line a 23 x 33cm/9in x 13in Swiss roll tin or small roasting tin with greaseproof paper.
Beat the eggs, sugar and vanilla in large bowl with an electric whisk until the mixture is very pale yellow, foamy and mousse-like. Fold in the warm water with a large metal spoon. (This helps prevent the Swiss roll from cracking when you roll it later.)
Sift over the flour and salt and fold in gently with the metal spoon. (Don’t overmix here or you will knock out the air and the Swiss roll will lose its sponginess. The trick is to incorporate all the flour with as few ‘folds’ as possible.)
Pour the mixture into the prepared tin and level it gently with a palette knife or the back of a large spoon. Bake in the oven for 10–15 minutes, or until the sponge has shrunk a little from the sides of the tin and feels springy to the touch. Remove the sponge from the oven and turn the cake out onto a sheet of baking paper sprinkled with caster sugar. Leave to cool for 10 minutes, then gently peel the lining paper off the sponge and leave to cool completely.
Meanwhile, for the mascarpone cream, mix all of the ingredients together in a large bowl.
To assemble the cake, trim off any rough edges of the sponge with a sharp serrated knife to get the sides nice and tidy. Spread the mascarpone cream all over the sponge, leaving a small margin so it does not squelch out when it is rolled. Spoon the macerated strawberries over the mascarpone filling and drizzle with a third of the strawberry purée (reserve the rest).
With the shortest side facing you, begin to roll up the sponge (away from you) using the baking paper to help. Try to do it as tightly as you can for an impressive-looking finish. Once you have rolled it all up, make sure the join is underneath so it does not come undone. Carefully lift onto a serving plate - you can do this with your hands or use two fish slices or spatulas.
Sprinkle with some caster sugar and decorate with extra sliced strawberries. Serve in slices with the remaining strawberry sauce drizzled over.