1.Combine yeast, sugar and milk in large bowl, whisk until yeast is dissolved. Stir in flour, cover, stand in a warm place about 40 minutes or until mixture has doubled in size. Beat butter, essence, extra sugar and salt in small bowl with electric mixer until light and creamy, beat in eggs 1 at a time. Stir butter mixture and sifted extra flour into yeast mixture in 2 batches.
2.Turn dough onto floured surface, knead about 10 minutes or until smooth and elastic. Place dough in large greased bowl, cover, stand in warm place about 1½ hours or until doubled in size.
3.To make walnut filling, combine butter, milk and coffee in small bowl; mix well. Stir in remaining ingredients.
4.Turn dough onto floured surface, knead until smooth. Roll dough to 20cm x 40cm rectangle. Spread walnut filling over dough, roll up from long side as for Swiss roll. Brush 1 end of roll with water.
5.Grease and flour 21cm baba pan. Place roll in pan, seam towards centre of pan. Gently press dough into pan; press ends together to join. Cover pan, stand in warm place until dough is risen to within 1cm from rim of pan. Preheat oven to 190°C.
6.Bake 10 minutes, reduce heat to 180°C, bake about 40 minutes. Serve dusted with icing sugar, if desired.