In a mixing bowl, combine warm milk, sugar, and instant yeast. Stir gently and let it sit for about 5-10 minutes until frothy.

In another bowl, combine 2 ½ cups flour and salt. Add the frothy yeast mixture along with melted butter, egg, and vanilla extract. Mix until well combined.

Knead the dough on a lightly floured surface until smooth and elastic, about 5-10 minutes. Place the dough back into the bowl, cover it with a cloth, and let it rise for 1 hour in a warm place.

In a separate bowl, mix together 1 ½ cups of flour, ¾ cup of sugar, and cinnamon. Use your fingers or a pastry cutter to blend in cold cubed butter until the mixture resembles coarse crumbs. Chill the streusel in the refrigerator.

After the dough has risen, roll it out on a floured surface and transfer it to a greased baking dish or pan. Evenly spread the streusel topping over the dough.

Preheat the oven to 350°F (175°C) and bake for 25–30 minutes, or until golden brown on top.