Step 1: In a large bowl, dissolve yeast in warm milk with a pinch of granulated sugar. Let stand for 5-10 minutes until foamy.
Step 2: Stir in the remaining 1/4 cup granulated sugar, egg, melted butter, vanilla extract, and salt into the yeast mixture.
Step 3: Gradually add 3 1/2 cups of flour, mixing until a shaggy dough forms. Turn the dough out onto a lightly floured surface.
Step 4: Knead the dough for 6-8 minutes, adding more flour a tablespoon at a time if the dough is too sticky, until it's smooth and elastic. It should pass the windowpane test.
Step 5: Place the dough in a lightly oiled bowl, turning once to coat. Cover with plastic wrap and let rise in a warm place for 1-1.5 hours, or until doubled in size.
Step 6: While the dough rises, prepare the filling: In a small bowl, cream together the softened butter, brown sugar, and ground cinnamon until well combined.
Step 7: Once the dough has risen, punch it down gently and turn it out onto a lightly floured surface. Roll the dough into a 16x10 inch rectangle.
Step 8: Spread the cinnamon-sugar filling evenly over the dough, leaving a small border (about 1/2 inch) around the edges.
Step 9: Starting from a long side, carefully roll the dough into a tight log. Pinch the seam closed to seal.
Step 10: Carefully transfer the log to a greased 9x5 inch loaf pan. Cover lightly with plastic wrap and let rise again in a warm place for another 30-45 minutes, or until noticeably puffy.
Step 11: Preheat your oven to 375°F (190°C).
Step 12: Bake for 30-35 minutes, or until the top is golden brown and an inserted toothpick comes out clean. If the top browns too quickly, tent loosely with foil.
Step 13: Let the bread cool in the pan for 10 minutes before carefully transferring it to a wire rack to cool completely.
Step 14: Prepare the glaze: In a small bowl, whisk together the powdered sugar, milk (or cream), and vanilla extract until smooth. Drizzle generously over the cooled bread.