In a large bowl or stand mixer with a dough hook, combine flours, sugar, yeast and salt. Stir to mix. Put milk and butter in a small pan over low heat, stirring occasionally until butter is melted. Remove from heat and let cool for two minutes. Stir in eggs and add to flour mixture, stirring until a soft dough forms. Knead with mixer or by hand for about 5 minutes. Dough will be soft; add a little flour as needed if the dough is too sticky to handle.
Transfer dough to a large bowl lightly coated with butter, turn to coat dough, and cover with a damp towel. Place in a warm spot to rise for about 90 minutes or until dough doubles in size.
Make the filling: In a double boiler over simmering water, place the chocolate and butter and stir occasionally until melted. Remove from heat and stir in tahini, then add powdered sugar and cocoa. Let cool to room temperature.
Lightly flour counter and butter a 9x13-inch pan. Transfer the dough to the floured counter and roll out into a 12x18-inch rectangle with the long edge facing you. Spread the chocolate mixture evenly over dough leaving 1/2 inch of the far long edge of the dough bare. Scatter dried cherries on top of the chocolate mixture, then carefully roll up the dough starting from the long edge nearest you to the other long edge. Cut the rolled dough into 12 equal rounds. Place rolls in the buttered pan. Whisk remaining egg with a tablespoon of water and brush tops of rolls. Cover with a damp towel, and allow to rise in a warm spot for an hour.
Heat the oven to 350°F. Once the rolls have risen, remove the towel and brush again with egg wash. Bake for about 30 minutes, until golden brown. Cool for at least 5 minutes before serving.