Dissolve yeast in warm water. Stir in sugar, salt, butter, eggs, yams, and enough flour to make soft dough. Turn dough onto a lightly floured board and knead for 5 minutes, or until smooth and elastic. Place in greased bowl; then cover and refrigerate until about 2 hours before serving time. (If using immediately, continue on to next step.)When ready to shape dough, divide it into 4 parts. Roll each part into a 12-inch circle. Spread each circle with melted butter cut into 12 pie-shaped pieces. Roll loosely, starting with large end. Place on greased baking sheet and allow rising until double in bulk. Bake for 15 to 18 minutes, or until lightly browned.