In a small bowl, whisk together egg yolks, salt and pepper. Make a well in the center of the potatoes, and add the egg mixture to the well. Stir to combine. Add ¾ cup of flour and 2 tablespoons of the pesto, stirring just until combined. Turn out onto a lightly floured surface. Knead in just enough of the remaining flour, if needed, to make a smooth, fairly soft dough. To keep the gnocchi light, do not overknead or add too much flour.