In a small bowl, mix together the water, milk, yeast and teaspoon of sugar and set aside until the mixture becomes foamy. Meanwhile, in a stand mixer with a dough hook, stir together the eggs, remaining sugar, salt, butter, sweet potato and rosemary. Add in the yeast mixture and half of the flour and stir until moistened. Add in the remaining flour gradually until the dough is soft and pulls away from the side of the bowl. Turn out the dough onto a lightly floured surface and knead briefly and shape into a tight ball. Place in a lightly greased bowl and allow to rise in a warm place until doubled (should take about an hour).
Remove the dough from the bowl and place on a flat surface. Cut the dough into 16 equal pieces and shape each piece into a tight ball. Place the balls in a 13x9 baking dish that has been greased and lined with parchment paper. Cover and allow the rolls to rise for another hour.
Preheat the oven to 350 degrees and bake for 20-25 minutes or until the rolls are browned and the internal temperature has reached 195 degrees.
Whisk the maple syrup and butter together until creamy and brush over the tops of the warm rolls. Sprinkle with sea salt and serve.
Tip: Make this recipe the day before! Shape the rolls and keep them in the fridge before baking. Take them out a couple hours before you bake them to rise.