In a small mixing bowl, whisk together the filling ingredients – butter, sugar, salt, vanilla extract and cinnamon powder. Butter should be at room temperature, otherwise you will not be able to spread it. (This can be prepared in advance too)
Using an offset spatula, spread the cinnamon mixture over the rolled-out dough. Don’t be shy, spread it all over to the edges.
Roll the dough gently, in a log (widthwise) and pinch the edges to seal. Cut the roll into 6 pieces. If you are using a round pan, you can cut it in 7 pieces too. The pieces should be equal in size, approximately 2 inches.
Place the cut sides down on a lightly greased deep dish or baking pan. (it’s important to use slightly deep dish as these will rise while proofing and baking) Leave some space in between them to rise.
Cover them with a plastic wrap and let them rise in a warm place until they have doubled in size for about 1 – 1 1/2 hours. You can visibly see, they would have doubled, would look puffy and the space in between them will be filled up.
After the rolls have risen, pre-heat the oven to 350 F. Place the buns in the preheated oven and bake them until they have golden edges and top, for 30 minutes. Every oven is different, so you might need few extra minutes or few minutes less.
Once baked, remove them from oven. Let the pan cool on a wire rack.