Soften yeast in warm water.
Combine milk, prune liquid, salt, sugar, and shortening; cool till lukewarm.
Add 2 cups flour; beat until smooth and elastic.
Add softened yeast and prunes; mix.
Add remaining flour or enough to make soft dough.
Turn out on a lightly floured surface; knead till smooth, about 10 minutes.
Shape in a ball; place in a greased bowl, turning once to grease surface.
Cover; let rise till double, 2 hours.
Turn out and divide dough in half; let rest 10 minutes.
Shape into 2 loaves.
Place in two greased 8 1/2 x 4 1/2 x 2 1/2-inch loaf pans.
Cover; let rise till double, 50 to 55 minutes.
Bake in moderate oven (375°) about 40 to 45 minutes.
Turn out of pans while hot.
Brush sides and top with butter.