In a bowl, combine 1-1/2 cups flour, sugar, salt and yeast. Heat milk, water and 4 tablespoons butter to 120°-130°. Gradually add to dry ingredients; beat on medium for 2 minutes. Add eggs and 1/2 cup flour; beat on high for 2 minutes. By hand, add enough remaining flour to form a soft dough.
Turn onto a floured surface; knead until smooth and elastic, about 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.
Punch dough down. Divide in half. Roll each half into a 26-in. x 8-in. rectangle. Melt remaining butter; brush over dough. Combine filling ingredients; sprinkle over butter. Roll up jelly-roll style form long end; pinch to seal. Place seam side down on greased nonstick baking sheets or baking sheets lined with parchment. Shape each roll into heart; seal ends. Cut from outer edge two-thirds through cake every 1 in. and turn each section out. Cover and let rise until doubled, about 1 hour.
Bake at 350° for 15-20 minutes or until golden. Remove immediately from baking sheets to wire racks. Cool completely; remove parchment if used. For glaze, cream sugar and butter. Stir in milk and vanilla until smooth. Drizzle over hearts.
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