Mix flours and sugar in mixer bowl. In a separate container dissolve the yeast in 300 grams of the water. Add the water and yeast to the flour and mix until the dough begins to come together. Add the salt, keep mixing, and add the butter in stages. Adjust the dough with the remaining water in order to achieve the right texture and elasticity.
To Assemble and Serve:
Proofing and baking times and temperatures vary. Potential fillings include red beet, fennel and onion, rosemary and raisin, and black cabbage.