In a small saucepan, heat milk, water and butter until very warm. In a large bowl combine heated liquids, 1 1/2 cups flour, sugar, salt and yeast. Beat 3 minutes at medium speed. Stir in additional 1 1/2 to 2 cups flour to form a soft dough. On a floured surface, knead the dough untill smooth and elastic<about 5 minutes>. Place dough in a greased bowl and cover. Let rise in a warm place for 30 to 45 minutes or until doubled in size. Grease a 12 cup fluted tube pan; sprinkle with poppy seeds. In a small saucepan saute onion in butter till lightly browned; stir in remaining filling ingredients Punch down dough; roll out to a 16x8-inch rectangle. Spread filling to abou 1-inch from edges. Start with the longer side, roll up tightly and seal edg Form into a circle and seal ends. Place in prepared pan. Cover and let rise about 15 minutes or til doubled in size. In a preheated 400F oven bake 20 to 30 minutes or untill golden brown. Remove immediately from pan.