1. Cut the sweet potatoes into 1 1/2-inch slices. Place the potato slices in a medium saucepan, and cover with water. Bring to a boil, reduce to a simmer, and cook until potatoes are tender. Drain and mash well.

2. In the detached bowl of an electric mixer, whisk yeast, 1/4 cup warm water (105 degrees), and a pinch of sugar. Set the mixture aside until foamy, about 6 minutes. Attach bowl to mixer fitted with the dough-hook attachment. On low speed, add mashed potatoes, milk, 1/2 cup melted butter, eggs, sugar, and salt. Slowly add flour to make a slightly sticky dough. Knead until smooth, about 2 minutes. Brush inside of a mixing bowl with butter. Place dough in bowl; cover with buttered plastic wrap. Set aside to rise until doubled in size, 1 1/2 to 2 hours.

3. Line 3 large baking sheets with parchment. Using a floured rolling pin on a floured work surface, roll dough out to 3/4 inch thickness. Cut rounds of dough as close together as possible with a 2 1/4-inch round cookie cutter. Scraps can be re-rolled once. Place rounds 1 to 2 inches apart on prepared baking sheets. Brush the tops with the remaining butter; cover with plastic wrap. Set aside to rise until light and they do not spring back when pressed with a finger, about 30 minutes.

4. Heat oven to 400 degrees. Bake until biscuits are golden brown, about 14 minutes. Cool on a wire rack for about 5 minutes before serving.