In small bowl, stir together yeast, oil, sugar, and about 3 tablespoons water until smooth. Stir in remaining water. In large bowl of a standing electric mixer fitted with dough hook whisk together 2 1/2 cups of all-purpose flour, whole-wheat flour, and salt. With mixer on low speed stir in yeast mixture and blend until mixture forms dough. With mixer on medium speed knead dough, adding enough of remaining 1 cup flour as necessary to prevent dough from sticking, until smooth and elastic, about 5 minutes. Put dough in an oiled deep bowl and turn to coat with oil. Let dough rise, loosely covered with plastic wrap, in a warm place 1 hour, or until doubled in bulk, and punch down. Divide dough into 6 balls. On a lightly floured surface roll out each ball of dough into a 9 1/2-inch round and stack, lightly floured, between sheets of parchment paper. Dough may be made 8 hours ahead and chilled, tightly wrapped in plastic wrap. Preheat oven to 550 degrees F. Spread 1 cup robiola on each round of dough, leaving a 1/2 inch border around the edge. Place another piece of thin, rolled out dough on top. Dock pizza all over so cheese can ooze through. Sprinkle 1-tablespoon semolina on each of 2 baking sheets and transfer 1 pizza to each. Bake in batches in lower third of oven 10 minutes, or until crust is crisp and golden. Transfer pizzas to plates and drizzle each with 1-tablespoon truffle oil and shaved truffles. Top and bake remaining pizzas in the same manner.