In a large mixing bowl, dissolve yeast in warm water. In another bowl combine milk, lard, salt and sugar. Heat to 110 degrees and add to dissolved yeast. Beat in 3 cups of the all purpose flour and all of the whole wheat flour. Add abut 1/2 c all purpose flour and mix until a stiff sticky dough forms. Place dough on a floured board and knead, adding more flour as needed, until dough is smooth and non sticky. Place dough in a greased bowl turning over to grease top. Cover and let stand at room temp. 1 hour. Punch dough down. The dough may be covered and chilled as long as overnight. Knead dough on a lightly floured board to expel air. Roll dough out, a portion at a time, to slightly less than 1/8" thick. Cut in 2"X 5" rectangles or 3" squares for appetizers. Place on lightly floured pans and lightly cover. If you work quickly you can let cut sopaipillas stay at room temp up to 5 min; otherwise, refrigerate them until all are ready to fry. In a deep wide frying pan or kettle heat 1 1/2 - 2 inches oil to 350 on a deep fat frying thermometer. Fry 2 or 3 at a time. When the bread begins to puff, gently push the bread into the hot oil several times to help it puff more evenly. Turn several times and cook just until pale gold on both sides, 1-2 minutes total. Drain on paper towels. Serve immediately or place in a warm oven until all are fried. Or if made ahead, cool, cover and chill or freeze. To reheat, bake uncovered in a 300 oven, turning once, just until warm, 5-8 min. Do not overheat or they will become hard. Makes 2 dozen large sopaipillas or about 4 dozen small ones.