Heat oven to 425 F. In a medium bowl, pour diced sweet potatoes and water and cover with plastic wrap. Microwave for 10 minutes or until tender. Remove from microwave; mash and set aside. In a medium bowl, finely chop kale and massage with olive oil. Stir honey into chopped kale and set aside. In a large bowl, stir self rising flour, sugar and salt together. Add 1 cup butter and vegetable shortening; with a pastry blender or fork, blend into flour mixture until it resembles coarse meal. Cover and chill for 10 minutes. Whisk the buttermilk and mashed sweet potatoes together and stir in kale. Add to flour mixture, stirring only until dry ingredients are moistened. Turn dough onto a well floured surface and knead lightly 3 or 4 times. Pat or roll dough to 3/4 inch thickness. Cut with a 2-inch round cookie cutter, reshaping scraps once. (Do not twist cutter.) Place dough rounds on parchment paper-lined baking sheets. Bake for 18 – 20 minutes or until biscuits are golden brown. Meanwhile, melt the remaining butter. Remove biscuits from oven and brush with melted butter. Serve immediately.