Start with the dough. Mix the yeast, sugar, milk and 100g flour together in a large bowl. Set aside in a warm place for 10 minutes.
Stir in the whole egg, egg yolk, vanilla extract, remaining 300g flour, melted butter and salt.
Knead using a dough hook or by hand, for about 8 minutes, until the dough is smooth and elastic.
Cover the bowl with clingfilm or a damp tea towel and leave to rise in a warm place for about 1 hour, or until doubled in size.
Make the filling while the dough rises. Cover the poppy seeds with plenty of water in a saucepan. Bring to the boil and simmer for about 40 minutes, making sure the water doesn’t run dry.
Drain and puree in a blender or food processor with the egg white, almonds, honey, vanilla extract and sugar. Stir in the raisins.
Preheat the oven to 180°C, 160°C fan, 350°F, Gas Mark 4.
Roll the dough out on a lightly floured surface to form a 30 x 40cm rectangle.
Spread the filling over evenly, leaving a 3cm border all around. Fold the top third of the dough over towards the centre – lengthwise – then fold the bottom third upwards, tucking the edge under to form a long log. Tuck the ends under, pinching the dough together to seal it. Transfer to a baking sheet lined with nonstick baking paper and brush the dough with the remaining egg white.
Bake for about 50 minutes, until deeply golden and risen.
Cool on a wire rack before slicing and serving.
Freezing and defrosting guidelines
Bake according to the recipe but stop before adding decoration or icing if called for. Allow to cool completely. Wrap well in clingfilm and tin foil (to prevent freezer burn) and freeze for up to 3 months.
Loosen the tin foil and clingfilm but leave to defrost in packaging at room temperature for several hours before serving.