Step 1

Pre-heat the oven to 355 ºF (180 ºC) and line a 10 x 15 inch (25 x 38 cm) baking tray or sheet with baking/greaseproof paper.

Step 2

In a heat-proof bowl above a pot of simmering water, melt the chocolate and butter together smooth and glossy. Set aside and allow to cool slightly.

Step 3

In a stand mixer with the whisk attachment, or with a hand mixer with the double beater attachments, whisk together the eggs and sugar until pale, fluffy and about tripled in volume.

Step 4

Add the melted chocolate and whisk for a few seconds until fully incorporated.

Step 5

Sift together the dry ingredients (gluten free flour blend, xanthan gum, cocoa powder, baking powder, baking soda and salt), and fold them gently into the fluffy chocolate mixture, until no flour clumps remain.

Step 6

Transfer to the lined baking sheet and bake at 355 ºF (180 ºC) until an inserted toothpick comes out clean (about 10 - 12 minutes).

Step 7

Once baked, leave the sponge in the baking tray for 2 minutes, then turn it out of the baking tray onto a piece of baking paper generously dusted with powdered sugar. Peel away the top layer of baking paper, and roll up the sponge. Leave it cool completely.

Step 8

In a big bowl, whip together heavy/double cream and powdered sugar until soft peaks form. You can use a stand or hand mixer – or even do it by hand.

Step 9

Once at the soft peak stage, fold in the mascarpone cheese. You will get a  smooth filling that spreads easily but will also hold its shape.

Step 10

Place the chopped dark chocolate into a heat-proof bowl.

Step 11

In a saucepan, bring the heavy/double cream to a boil, then pour it over the chocolate. Allow this to stand for 2 - 3 minutes, then stir until smooth. You should get a smooth runny ganache that's easily pourable.

Step 12

Gently unroll the cooled sponge, and spread the filling into an even layer onto top.

Step 13

Carefully re-roll the sponge, and chill it in the fridge for about 1/2 hour.

Step 14

Once chilled, drizzle the Swiss roll with the chocolate ganache glaze. (If the glaze is to firm, reheat it briefly in the microwave or over some simmering water.)

Step 15

Allow the chocolate ganache glaze to set, and enjoy!

Step 16

The chocolate Swiss roll keeps well for 3 - 4 days in a cool dry space (the fridge works too), wrapped in cling film or in a closer container.