Start by making the roll-in. Mix the margarine and flours well then spread out onto a sheet of cling wrap. Spread out roughly then top with another sheet of cling wrap. Using a rolling pin, roll the fat out until 1/2cm thick to make 30 x 20cm rectangle. Close the ends of the cling wrap and place in the freezer until hard.
In the meantime, prepare the dough by mixing the yeast and 100g of water in a mixing bowl. Cover and place in a warm place until frothy. Then add the rest of the ingredients and combine in the bowl of a mixer using the dough hook attachment. Knead for about 4 minutes then allow the dough to rest for 20 minutes.
Roll the dough out on a floured surface to 1cm thick then place the chilled butter roll-in on top. Do a simple 3-fold (like folding a business letter) and roll out again to 1cm thick. Cover and place in the freezer to rest for 20 minutes. Roll the dough out once again to 1cm thick then do another 3-fold. Rest again in the freezer for 20 minutes before doing the last fold and rest.
Roll the dough out again to 1cm thick and cut out with a round cookie cutter and a smaller one, to create the hole in the centre. Place the pastry circles onto a lined and floured baking sheet, cover lightly and allow to proof in a warm place until doubled in size.
Preheat the oil to 165C and deep-fry the cronuts in batches until golden and puffed. Drain on paper towel and allow to cool completely. If you would like to dredge them in sugar, do so while hot.
To assemble, poke 3 holes in the bottom of each cronut with a chopstick or knife then pipe vanilla pastry cream into the bottom of each. Dip the tops in a glaze flavoured with orange blossom water and allow to set. Serve immediately.