In a large bowl, add in the milk, brown sugar, and yeast, and mix using your hand mixer until well combined.

Add in the flour, butter, eggs, vanilla, and salt. Now, mix together properly until the flour is fully incorporated into the mixture.

Cover the bowl with a plastic wrap, and allow the dough to sit for about 1 hour or until it has doubled in size.

Now, prepare the filling. In a small bowl, add in the cinnamon powder, granulated sugar, and brown sugar and mix properly.

Now, punch the dough down, and roll it out on a floured surface to avoid sticking. Allow it to roll into a flat rectangular shape, then spread the butter evenly over the dough and sprinkle on the cinnamon and sugar mix.

With the longer side, start rolling the dough into a log, keeping it tightly packed together as you go. When you reach the edge, pinch along the edge to seal it with the last rolled part.

Using a sharp knife, cut the log into 12-15 rolls, and place on a buttered baking pan. Cover with plastic wrap and allow to rise for about 20 minutes.

Preheat your oven to 350°F (or 180°C), and bake for about 20 minutes or until golden brown.

Now, prepare the icing. In a medium bowl, add the Confectioners' sugar and whisk in the melted butter, milk, and vanilla extract. Mix together until smooth.