Mix water, milk, sugar, and yeast in the bowl of a stand mixer and let bloom for thirty minutes. Add the whole wheat flour and 2 cups of the bread flour and mix until it forms a thick batter. Add the butter and salt and mix until incorporated. Switch to the dough hook and add the remaining flour. The dough should clear the sides of the bowl and cling to the dough hook. Knead on medium speed for 5 minutes.Transfer the dough to a lightly oiled bowl, turning once to coat. Cover the bowl and set aside to rise until doubled in volume, about 90 minutes. Turn the dough out onto a lightly floured surface and divide into 4 equal portions. Roll each piece of dough into a sandwich roll and set on a parchment lined baking sheetCover the baking sheet with a damp kitchen towel and set aside to rise for 30 minutes. Meanwhile. mix the toppingTOPPINGWhisk together yeast, sugar, and water and bloom for thirty minutes.Add the oil, salt, and rice flour and whisk until combined. Set the topping aside for 20 minutes until bubbly.Preheat the oven to 400°F and place rack on the top level of the oven.Brush the topping generously onto the the rolls. Let the rolls rise another 20 minutes.Bake until golden brown, about 22-27 minutes. Let cool completely.