You will need
In a medium-sized bowl, combine water, yeast and 20g of the caster sugar. Let it sit for 5-10 minutes until frothy.
In a separate electric mixer bowl with a dough hook, mix Rustic White Bread Mix, salt and the remaining caster sugar. Add vinegar, eggs, warm milk and yeast mixture. Combine all ingredients.
Add cubed butter to the mixture, and mix until the butter is no longer visible. This will result in a nice dough ball.
Put the dough in a clean bowl, cover it and let it rise in a warm place until it doubles in size. If not using straight away, you pop it in the fridge for using the next day. Get it out in a couple of hours before and let it warm up to room temperature.
Once the dough has risen, roll it out on a baking mat or baking paper. Lightly flour the surface and place the dough in the center. Make three indentations by pressing down with a rolling pin. Turn the dough and continue rolling, lightly dusting with flour and turning to prevent sticking.
Roll out to a thickness of about 1cm, in a 30 x 20cm rectangle.