In a stand mixer bowl (or large bowl), combine 1 ½ cups flour, sugar, yeast, and salt. In a separate bowl, whisk together milk, water, egg and melted butter. Add wet ingredients to dry ingredients and mix until a shaggy dough forms.
Knead: Switch to a dough hook attachment (or knead by hand on a floured surface) and knead for about 8-10 minutes until a smooth, elastic dough forms. Add the remaining flour if the dough is too sticky.
First Rise: Lightly grease a large bowl. Place the dough inside, cover it with plastic wrap or a damp kitchen towel and let rise in a warm spot for 1-2 hours, or until doubled in size.
Make the Filling: While the dough rises, combine softened butter, brown sugar, and cinnamon in a bowl. Set aside.
Shape: Punch down the risen dough. Roll it into a large rectangle (about 12×18 inches) on a lightly floured surface. Spread the cinnamon-sugar filling evenly over the dough. Roll the dough up tightly starting from the long end. Cut into 12 even rolls.
Second Rise: Grease a 9×13-inch baking dish. Place rolls into the dish, cover loosely and let rise in a warm spot for 30-60 minutes, or until puffy.
Second Rise: Grease a 9×13-inch baking dish. Place rolls into the dish, cover loosely and let rise in a warm spot for 30-60 minutes, or until puffy.
Bake: Preheat oven to 375°F (190°C). Bake honey buns for 20-25 minutes, or until golden brown.
Make the Glaze: While the buns bake, whisk together powdered sugar, honey, melted butter, vanilla extract, and hot water until smooth. Start with 2 tablespoons of water, adding more if needed for desired consistency.
Glaze and Serve: As soon as the honey buns come out of the oven, generously drizzle the glaze over them. Serve warm.