Put 500 grams/4 cups strong white flour, 300 grams/10 oz unsalted butter, 8 grams/0.3 oz fine salt, 2 x 7 grams yeast packets, 50 grams/1.75 oz caster sugar in a free standing mixer or large mixing bowl and add the 300 mls milk with the dough hook running until it comes together. If not using a free standing mixer then stir hard with a wooden spoon. You may have to add a touch more milk. The dough should be a little tacky.
Knead for a couple of minutes either with your dough hook or on a work surface before putting in a clean oiled bowl and covering with cling film. Put in the fridge overnight.
Draw out a rectangle 20 cm x 19 cm on grease proof paper and put your slightly soft butter cut lengthways into the middle. Cover with cling film and use a rolling pin to squash/roll out to fit. Cover and chill over night.
Take out the dough and roll out to a rectangle 60 cm x 20 cm. Take out the butter and trim the edges to size. Put the butter in the middle of the dough. Fold the first flap over the butter followed by the second flap on top of that. Seal the butter in the parcel with your fingers.
Carefully roll out the square of dough to a rectangle roughly 60 cm x 20 cm again. Fold into three, cover and chill for at least 30 minutes.
Repeat another three times. If the butter becomes too soft at any time just chill for longer than the thirty minutes. I have even put mine in the freezer for ten minutes.
After the final roll cut down the middle with a pizza cutter or sharp knife and then cut each strip into 10 cm squares. Working quickly pop your chocolate into the middle and roll up into a sausage and place onto a lined baking tray. You will need two baking trays. Cover and prove somewhere cool until very puffy.
Preheat your oven to 200 C electric- 180 C fan - Gas Mark 6
Brush with egg wash and bake for about 20 minutes. Cool on a wire rack.
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