Grease your swiss roll tin, then line it with baking paper, ensuring it fits well to get the desired shape. Preheat your oven to 180°C Fan (200°C conventional) so it's ready for baking.

Using an electric hand whisk, beat the granulated sugar and eggs together until the mixture is light and frothy, which should take a few minutes. Sift in the gluten-free self-rising flour, xanthan gum, and sifted cocoa powder. Gently fold these dry ingredients into the egg mixture until just combined. Pour the batter into your prepared tin, spreading it evenly to the edges as the mixture will be thin. Bake for about 9 minutes, until the sponge has slightly risen and starts to come away from the sides. I always check that the sponge springs back gently when pressed.

Remove the sponge from the oven and carefully invert it onto another piece of baking paper on a flat surface. Peel off the baking paper used for lining. While still warm, gently roll the sponge up with the new paper inside. Prop it against a heavy object to keep it tight and let it cool completely while rolled—this helps prevent cracks.

Whip the cold heavy cream with powdered sugar until it forms soft peaks. Fold in 2 to 3 tablespoons of Baileys, tasting and adjusting for flavor. This creamy filling adds a lovely richness; I always taste at this stage and sometimes add an extra splash of Baileys for a more pronounced flavor.

Melt the dark chocolate and set aside to cool slightly. In a stand mixer or with an electric hand whisk, beat the softened butter on high for about 5 minutes until it turns pale. Gradually add the powdered sugar in two stages, beating each addition for 3-5 minutes. Add the melted and cooled chocolate, then mix until fully combined and smooth.

Gently unroll the cooled sponge. Spread a layer (about 1cm thick) of the Baileys cream filling from Step 4 over the sponge, leaving about half a centimeter around the edges to prevent overfilling. Carefully roll the sponge back up tightly and transfer it to your serving board. I like to use a tea towel to help roll it tightly for the best swirl.

Spread the chocolate buttercream from Step 5 evenly over the rolled Swiss roll. Use a fork or sharp knife to create a wood-like texture. Finish by dusting with a little powdered sugar, then decorating with Baileys truffles and grated white chocolate for a festive touch.