In a small bowl, dissolve yeast in warm water. In a large bowl, combine the milk, butter, 1/3 cup sugar, egg yolks, salt, yeast mixture and 3 cups flour; beat until smooth. Stir in enough remaining flour to form a soft dough (do not knead)

Place in a greased bowl, turning once to grease top. Cover and let rise in a warm place until doubled, about 45 minutes.

Punch dough down. Turn onto a lightly floured surface; knead about 10 times. Divide dough in half.

Roll each portion to 1/4-in. thickness; cut with a floured 2-1/2-in. round cutter.

Place on greased baking sheet. Cover and let rise until doubled, about 45 minutes.

In an electric skillet or deep-fat fryer, heat oil to 375°. Fry doughnuts, a few at a time, for 1-2 minutes on each side or until golden brown. Drain on paper towels. Roll warm doughnuts in remaining sugar. Use pastry bag and long tip to inject jam. Yield: 16 doughnuts.