Place the flour, salt, yeast and sugar in the bowl of a food mixer with the dough hook fitted.
Crack the eggs into a jug and mix with a fork, then pour this into the flour mixture and beat on a slow speed for 6-8 minutes until the dough starts to come away from the sides of the bowl.
Take the butter and cut it into cubes and slowly add it to the mixer beating on medium speed until all of the butter has been incorporated. Make sure the butter has been mixed in before adding the next lot.
Mix on medium-high for 5 minutes until the dough is elastic and pulled away from the sides.
Place a towel or some cling-film over the bowl and leave it to prove for two hours or until doubled in size.
Then knock back the dough by knocking the air out of it and giving it a light knead.
Cover the bowl again with Clingfilm and place in the fridge overnight to rest.
To make the hazelnut praline paste, place the hazelnuts on a baking tray lined with greaseproof paper and roast in a pre-heated oven at 170C for about 10 minutes until golden and fragrant.
Place the sugar and water in a saucepan and cook over a low heat to dissolve the sugar. Increase the heat to high and cook the syrup to 116C.
Add the warm hazelnuts and stir to coat them evenly. Continue cooking the hazelnuts and syrup until they are a deep amber colour and no sandy white bits remain. Spread onto a baking sheet to cool completely.
To turn this into praline paste, put the caramelized hazelnuts in a food processor, blend until a smooth and runny paste forms this will take about 8 to 12 minutes. This recipe will make more than you need. Place the excess in a sterilised jar.
The next day, grease a standard loaf tin, divide the dough into 5 balls, approx. 205g each, roll the dough out to about 1cm thick and spread a layer of hazelnut praline paste leaving 1/2cm gap around the edge so the paste doesn't spill out, sprinkle with dark chocolate chips.
Roll up the dough, so that it is like a Swiss roll, then tuck the sides under to gently seal everything in, a bit like a 'u' shape.
place the mini loaf shape in the tin with the smooth side facing up and the sealed side on the bottom. Repeat with the four remaining balls of dough.
Cover lightly and leave somewhere warm to prove for 3 hours or until it has risen to the top of the loaf tin.
Then pre-heat the oven to 180C/160C Fan/Gas Mark and glaze with beaten egg bake for 35 mins, or until golden and crunchy to the touch.
Leave to cool and then remove from the tin, slice and eat.