Using the paddle attachment of your mixer, mix together the flour, butter, parmesan, thyme and a good pinch of salt.
Once well mixed, add egg yolk and water. Start with 3 tbsp and add an extra one if the dough is too dry.
At this point, make sure not to overmix, just enough to mix all the ingredients together. Make a ball with your dough, slightly flatten it, wrap it with plastic and keep in the fridge for 2 hours.