Bread Dough

• Add bread flour, caster sugar, salt, active dry yeast, beaten egg, and milk to a large mixing bowl. Knead the ingredients with a stand mixer attached to a dough hook until a dough forms. Add softened butter and continue to knead for 10 to 15 minutes until smooth and more elastic. (You may also knead the dough by hand).
• Cover the dough with plastic film and let it rise in a warm area for 40 minutes until doubled in size.
• Meanwhile, let's prepare the chocolate cake. Preheat oven to 302°F (or 150°C).
• Melt the butter and chocolate bar in a small pot over low heat, then transfer the mixture to a large bowl and let it cool down for a little bit. Next, whisk in milk, egg yolks, and sifted cake flour. Mix until no powder left. Do Not over mix the batter. Set the batter aside.
• Add the egg whites to a separate mixing bowl, and beat it with an electric hand mixer until foamy. Keep beating the egg white while adding the caster sugar in 3 batches, and continue to beat until stiff peak forms.
• Fold in 1/3 of the whisked egg white into the batter, and gently mix to combine well. Then, fold the mixture into the remaining whisked egg white and mix gently. Pour the batter into a 10" x 14" ( 25 x 35 cm)baking tin lined with parchment paper. Bake for 20 minutes.
• Once the cake is baked. Remove it from the oven and allow it to cool. Unmold it and remove the parchment paper. Trim the edges and set aside.
• Transfer the bread dough to a floured working surface. Roll out the dough into a rectangle slightly larger than the chocolate cake. Place the chocolate cake on top of the dough and roll it up tightly into a log. Pinch the edges to seal.
• Transfer the whole piece to a loaf tin greased with butter. Cover the tin with plastic film and let it rise for 45 minutes until doubled in size.
• Preheat the oven to 374°F (or 190°C). Brush with beaten egg and bake for 25 minutes until golden brown. Remove from the oven and cool down. Unmold and enjoy.