Preheat the oven to 180C/350F/Gas4
Place the yeast, half of the sugar and 2 tablespoons of the lukewarm milk/water combo in a small glass and cover. Let it sit for about 20 minutes so the yeast goes all frothy.
Sieve the flour, remaining sugar and salt into a large bowl and rub in the chilled butter to form a crumb mixture.
Make a well in the centre and pour in the yeast, half of the beaten egg and a little of the liquid.
Start stirring the mix together to form a dough and add more and more of the liquid as you go.
Turn dough out on to a floured work surface and knead for about ten minutes.
Use the olive oil to wipe round the inside of your bowl and also to coat the dough. Pop it into the bowl and cover with a damp tea towel.
Set aside in a warm place for 1 1/12 hours until it has doubled in size.
Tip out the dough and punch out the air (very satisfying!).
Pull into three pieces and roll out into long strips.
Cut your strips into four short lengths and braid into four plaited rolls.
Leave these on a baking sheet for another 20 minutes to rise some more.
Add a teaspoon of water to your remaining beaten egg and use this to glaze the rolls.
Scatter with the sesame seeds.
Bake for 15 - 20 minutes or until golden in colour. When you tap them underneith there should be a hollow sound.
Allow to cool on a wire rack.