Preheat the oven to 180°C and lay your hazelnuts out on a baking tray and roast between 7-10 mins.
Whilst the hazelnuts are warm, remove their skins, you can use a tea towel to slide the skins off and protect your fingers from the heat. Once cooled, roughly chop the hazelnuts and add them to a mixing bowl along with the rye flour and plain flour, baking powder, bicarbonate of soda and half (5g) of the sea salt flakes.
In a separate bowl, add the two sugars, olive oil and 80g water, and using a hand-held electric whisk, beat until smooth.
Once smooth, add the sugar mixture to the flour mixture and stir using a wooden spoon until combined.
Once all of the ingredients are combined freeze the cookie dough mixture for 30 mins or until firm.
Just before the end of the 30 minute freezing time, preheat your oven to 180°C (160°C fan-forced) & line two large oven trays with the silpat mats or baking paper.
Remove the dough from the freezer and using a trigger ice-cream scoop, scoop level balls of dough 5cm apart onto the prepared baking trays.
Bake cookies for 12 minutes or until golden around edges. Remove from oven, place the roughly chopped dark chocolate chunks over cookies, and return trays to oven for three minutes or until chocolate is partially melted.
Remove from the oven and transfer the baking trays to cooling racks and sprinkle with the remaining salt flakes.
Cool the cookies on trays for 10 minutes then Transfer to a wire rack to cool. Suitable to freeze.
