Combine 1-1/4 cups flour, sugar, undissolved yeast and salt. Heat water, milk and butter until very warm (120oF to 130oF). Gradually add to flour mixture. Beat 2 minutes at medium speed of electric mixer, scraping bowl occasionally. Add egg yolks and 1/2 cup flour; beat 2 minutes at high speed. Stir in enough remaining flour to make a soft dough.
Divide dough in half; roll half of the dough on lightly floured surface to fit the bottom of ungreased 15-1/2 x 10-1/2 x 1-inch jelly roll pan. Place in pan, pressing dough up sides. Spread with Apple Filling. Roll remaining dough large enough to cover filling. Place over filling; seal edges together. Snip surface of dough with scissors to let steam escape. Cover; let rise in warm, draft-free place until doubled in size, about 45 minutes.
Bake at 375oF for 20 minutes or until evenly golden. Drizzle with Powdered Sugar Glaze. Let cool in pan; cut into squares.
Apple Filling: Combine water, sugar, cornstarch, cinnamon, nutmeg and salt in large a large saucepan. Stir in egg yolk and apples. Cook over medium heat, stirring constantly until thick, about 5 minutes. Remove from heat; let cool.
Powdered Sugar Glaze: Stir powdered sugar and milk in a small bowl until smooth.