In a large bowl, dissolve yeast in milk. Add the butter, sugar, salt and 2 cups flour; beat until smooth. Stir in enough remaining flour to form a soft dough. , Turn onto a floured surface; knead until smooth and elastic, 6-8 minutes. Place in a greased bowl, turning once to grease top. Cover and let rise in a warm place until doubled, about 1 hour. , In a large bowl, beat egg and yolk; stir in cheese. Punch down dough; roll into a 16-in. circle. , Place in a greased 10-in. cast-iron skillet or 9-in. round baking pan, letting dough drape over the edges. Spoon the cheese mixture into center of dough. Gather dough up over filling in 1-1/2-in. pleats. Gently squeeze pleats together at top and twist to make a topknot. Let rise 10-15 minutes. , Brush loaf with egg white. Bake at 375° for 40-45 minutes. Cool on a wire rack for 20 minutes. Serve warm.